1. Field of the Invention
The present invention relates to a novel polymer having at least one type of acid labile group, terminally modified, and optionally crosslinked within a molecule and/or between molecules with crosslinking groups having Cxe2x80x94Oxe2x80x94C linkages. It also relates to a resist composition comprising the polymer as the base resin and a patterning process using the resist composition. This resist composition provides a much improved alkali dissolution contrast before and after exposure, high sensitivity, and high resolution, and in particular, is well reproducible as a micropatterning material for VLSI fabrication.
2. Prior Art
Deep-ultraviolet lithography, one of a number of recent efforts that are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, is thought to hold particular promise as the next generation in microfabrication technology. Deep-UV lithography is capable of achieving a minimum feature size of 0.5 xcexcm or less and, when a resist having low light absorption is used, can form patterns with sidewalls that are nearly perpendicular to the substrate.
Recently developed acid-catalyzed chemically amplified positive resists, such as those described in JP-B 27660/1990, JP-A 27829/1988, U.S. Pat. No. 4,491,628 and U.S. Pat. No. 5,310,619, utilize a high-intensity KrF excimer laser as the deep-UV light source. These resists, with their excellent properties such as high sensitivity, high resolution, and good dry etching resistance, are especially promising for deep-UV lithography.
Such chemically amplified positive resists include two-component systems comprising a base resin and a photoacid generator, and three-component systems comprising a base resin, a photoacid generator, and a dissolution regulator having acid labile groups.
For example, JP-A 115440/1987 describes a resist comprising poly-4-tert-butoxystyrene and a photoacid generator, and JP-A 223858/1991 describes a similar two-component resist comprising a resin bearing tert-butoxy groups within the molecule, in combination with a photoacid generator. JP-A 211258/1992 describes a two-component resist which is comprised of polyhydroxystyrene bearing methyl, isopropyl, tert-butyl, tetrahydropyranyl, and trimethylsilyl groups, together with a photoacid generator.
JP-A 100488/1994 discloses a resist comprised of a 20-polydihydroxystyrene derivative, such as poly[3,4-bis(2-tetrahydropyranyloxy)styrene], poly[3,4-bis(tert-butoxy-carbonyloxy)styrene] or poly[3,5-bis(2-tetrahydro-pyranyloxy)styrene], and a photoacid generator.
However, when the base resin in these resists bears acid labile groups on side chains and these acid labile groups are groups such as tert-butyl and tert-butoxycarbonyl which are cleaved by strong acids, the resin reacts with air-borne basic compounds and loses some of its activity, as a result of which cleavage of the acid labile groups arises less readily and the resist pattern tends to take on a T-top profile. By contrast, alkoxyalkyl groups such as ethoxyethyl are cleaved by weak acids, and so are little affected by air-borne basic compounds. Yet, their use also has its drawbacks, such as considerable narrowing of the pattern configuration as the time interval between exposure and heat treatment increases. Moreover, the presence of bulky groups on the side chains lowers the thermal stability of the resin, making it impossible to achieve a satisfactory sensitivity and resolution. These problems have hitherto prevented the practical implementation of either approach, and workable solutions have been sought.
The polymers described in JP-A 305025/1996 represent an attempt to resolve the foregoing problems, but characteristics of the production process render difficult the design of substituent ratios for acid labile groups and crosslinking groups. An additional shortcoming is that the production of these compounds results in the incidental formation of the crosslinking groups mentioned in JP-A 253534/1996. That is, in the design of resist compositions, polymers having various alkali dissolution rates are required, depending on the types and amounts of photoacid generators and additives selected, in addition to which the production of these polymers must be a reproducible process. However, the production methods described in the above prior-art references are subject to inherent limitations in the selection of acid labile groups and crosslinking groups, and in their substituent ratios.
It is, therefore, an object of the present invention to provide a novel and improved polymer which can be used as the base resin to formulate a chemically amplified positive working resist composition which is superior to prior-art resists in sensitivity, resolution, exposure latitude, process flexibility and reproducibility, and which forms a resist pattern having excellent plasma etching resistance and outstanding thermal stability. Another object of the invention is to provide a chemically amplified positive working resist composition comprising the polymer and a patterning process using the resist composition.
We have found that a novel polymer bearing at least one type of acid labile group, modified at terminals, and optionally crosslinked within a molecule and/or between molecules with a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage can be produced by a method to be described later and is useful as a base resin. By blending this novel polymer as a base resin with a photoacid generator and optionally, a dissolution regulator and a basic compound, there is obtained a chemically amplified positive resist composition which is improved in that the dissolution contrast of a resist film is increased, especially a dissolution rate after exposure is increased. By further blending an aromatic compound having a group xe2x95x90Cxe2x80x94COOH in a molecule, there is obtained a chemically amplified positive resist composition which is improved in that the resist is improved in PED stability and edge roughness on a nitride film substrate is improved. By further blending an acetylene alcohol derivative, the resist composition is improved in coating and storage stability, forms resists having high resolution, improved latitude of exposure, and improved process flexibility, and is well suited for practical use and advantageously used in precise microfabrication, especially in VLSI manufacture.
In a first aspect, the invention provides a styrene polymer represented by the following general formula (1), terminated with P, and having a weight average molecular weight of 1,000 to 500,000. 
Herein, R is hydroxyl or OR3 groups, at least one of R groups being hydroxyl, R1 is hydrogen or methyl, R2 is a normal, branched or cyclic alkyl group of 1 to 30 carbon atoms, R3 is an acid labile group, letter x is 0 or a positive integer, y is a positive integer, satisfying x+yxe2x89xa65, k is 0 or a positive integer, m is 0 or a positive integer, n is a positive integer, satisfying k+m+nxe2x89xa65, p and q are positive numbers satisfying 0 less than qxe2x89xa60.8 and p+q=1, with the proviso that the R3 groups may be the same or different when n is at least 2, xcex94 is such a number that the polymer may have a weight average molecular weight of 1,000 to 500,000, P is hydrogen, normal, branched or cyclic alkyl or alkenyl groups of 1 to 30 carbon atoms, aromatic hydrocarbon groups of 6 to 50 carbon atoms, carboxyl, hydroxyl, or groups of the following general formula (2), (3) or (4), all the terminal groups are not hydrogen at the same time, 
wherein R4 is (r+1)-valence aliphatic hydrocarbon groups or alicyclic saturated hydrocarbon groups of 1 to 30 carbon atoms, or aromatic hydrocarbon groups of 6 to 50 carbon atoms, R5 is normal, branched or cyclic alkyl groups of 1 to 30 carbon atoms, aromatic hydrocarbon groups of 6 to 50 carbon atoms, alkoxy groups of 1 to 30 carbon atoms, or hydroxyl, R5a is normal, branched or cyclic alkyl groups of 1 to 30 carbon atoms or aromatic hydrocarbon groups of 6 to 50 carbon atoms, letter h is 0 or 1, and letter r is a positive integer of 1 to 3.
The polymer of formula (1) may be crosslinked within a molecule and/or between molecules with a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage resulting from reaction of at least one of the phenolic hydroxyl groups represented by R in formula (1), the hydroxyl groups represented by R5 in formula (2), and the hydroxyl groups in formula (3) with an alkenyl ether compound or halogenated alkyl ether compound, and the amount of the acid labile group and the crosslinking group combined is on the average from more than 0 mol % to 80 mol % of the entirety of hydrogen atoms in the phenolic hydroxyl groups in formula (1), the hydroxyl groups represented by R5 in formula (2), and the hydroxyl groups in formula (3).
In one preferred embodiment, the polymer is represented by the following general formula (5): 
wherein R is hydroxyl or OR3 groups, at least one of the R groups being hydroxyl, R1 is hydrogen or methyl, R2 is a normal, branched or cyclic alkyl group of 1 to 30 carbon atoms, R3 is an acid labile group, R9 and R10 are hydrogen or normal, branched or cyclic alkyl groups of 1 to 8 carbon atoms, R11 is a monovalent hydrocarbon group of 1 to 18 carbon atoms which may have a hetero atom, or R9 and R10, R9 and R11, and R10 and R11, taken together, may form a ring, and each of R9, R10 and R11 is a normal or branched alkylene group of 1 to 18 carbon atoms when they form a ring, R12 is a tertiary alkyl group of 4 to 20 carbon atoms, a trialkylsilyl group whose alkyl groups each have 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group represented by xe2x80x94CR9R10OR11, letter a is an integer of 0 to 6, p1 and p2 are positive numbers, q1 and q2 are 0 or positive numbers, satisfying 0 less than p1/(p1+q1+p2+q2)xe2x89xa60.8, 0xe2x89xa6q1/(p1+q1+p2+q2)xe2x89xa60.8, 0 less than q2/(p1+q1+p2+q2)xe2x89xa60.8, and p1+q1+p2+q2=1, q1 and q2 are not equal to 0 at the same time, x, y, k, m, n, xcex94, and P are as defined above. In this embodiment, a hydrogen atom may be eliminated from at least one of the phenolic hydroxyl groups represented by R in formula (5), the hydroxyl groups represented by R5 in formula (2), and the hydroxyl groups in formula (3) to leave an oxygen atom which-is crosslinked with a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage of the following general formula (6a) or (6b) within a molecule and/or between molecules, and the amount of the acid labile group and the crosslinking group combined is on the average from more than 0 mol % to 80 mol % of the entirety of hydrogen atoms in the phenolic hydroxyl groups represented by R in formula (5), the hydroxyl groups represented by R5 in formula (2), and the hydroxyl groups in formula (3), 
wherein R6 and R7 each are hydrogen or a normal, branched or cyclic alkyl group of 1 to 8 carbon atoms, or R6 and R7 taken together, may form a ring, with the proviso that each of R6 and R7 is a normal or branched alkylene group of 1 to 8 carbon atoms when they form a ring, R8 is a normal, branched or cyclic alkylene group of 1 to 10 carbon atoms, letter d is 0 or an integer of 1 to 10, A is a c-valent aliphatic or alicyclic saturated hydrocarbon group, aromatic hydrocarbon group or heterocyclic group of 1 to 50 carbon atoms, which may have an intervening hetero atom and in which the hydrogen atom attached to a carbon atom may be partially replaced by a hydroxyl group, carboxyl group, acyl group or halogen atom, B is xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94NHCOxe2x80x94Oxe2x80x94 or xe2x80x94NHCONHxe2x80x94, letter c is an integer of 2 to 8, and cxe2x80x2 is an integer of 1 to 7.
More preferably, in formula (1) or (5), R3 is at least one member selected from the group consisting of a group of the following general formula (7) or (8), a tertiary alkyl-group of 4 to 20 carbon atoms, a trialkylsilyl group whose alkyl groups each have 1 to 6 carbon atoms, and an oxoalkyl group of 4 to 20 carbon atoms, 
wherein R9 and R10 are independently hydrogen or normal, branched or cyclic alkyl groups of 1 to 8 carbon atoms, R11 is a monovalent hydrocarbon group of 1 to 18 carbon atoms which may have a hetero atom, or R9 and R10, R9 and R11, and R10 and R11, taken together, may form a ring, and each of R9, R10 and R11 is a normal or branched alkylene group of 1 to 18 carbon atoms when they form a ring, R12 is a tertiary alkyl group of 4 to 20 carbon atoms, a trialkylsilyl group whose alkyl groups each have 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group represented by formula (7), and letter a is an integer of 0 to 6.
In the polymer according to the preferred embodiment, the crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage represented by the general formula (6a) or (6b) is typically represented by the following general formula (6axe2x80x2) or (6bxe2x80x2): 
wherein R6 and R7 each are hydrogen or a normal, branched or cyclic alkyl group of 1 to 8 carbon atoms, or R6 and R7, taken together, may form a ring, with the proviso that each of R6 and R7 is a normal or branched alkylene group of 1 to 8 carbon atoms when they form a ring, R8 is a normal, branched or cyclic alkylene group of 1 to 10 carbon atoms, letter d is 0 or an integer of 1 to 5, A is a cxe2x80x3-valent normal, branched or cyclic alkylene, alkyltriyl or alkyltetrayl group of 1 to 20 carbon atoms or an arylene group of 6 to 30 carbon atoms, which may have an intervening hetero atom and in which the hydrogen atom attached to a carbon atom may be partially replaced by a hydroxyl group, carboxyl group, acyl group or halogen atom, B is xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94NHCOxe2x80x94Oxe2x80x94 or xe2x80x94NHCONHxe2x80x94, letter cxe2x80x3 is an integer of 2 to 4, and cxe2x80x3 is an integer of 1 to 3.
In a second aspect, the invention provides a chemically amplified positive resist composition comprising
(A) an organic solvent,
(B) a base resin in the form of the polymer of any one of claims 1 to 4, and
(C) a photoacid generator.
The resist composition may further include (D) another base resin in the form of a polymer comprising recurring units of the following general formula (9), some of the hydrogen atoms of phenolic hydroxyl groups therein being replaced by acid labile groups of at least one type in an average proportion of 0 mol % to 80 mol % of the entirety, said polymer having a weight average molecular weight of 3,000 to 300,000. 
Herein, R1, R2, R9, R10, and R11 are as defined above, R12 is an acid labile group different from the xe2x80x94CR9R10OR11, e and f are 0 or positive numbers, g is a positive number, satisfying e+f+g=1, 0xe2x89xa6e/(e+f+g)xe2x89xa60.5, and 0.4xe2x89xa6g/(e+f+g)xe2x89xa60.9. The polymer of formula (9) may be crosslinked within a molecule and/or between molecules with crosslinking groups having Cxe2x80x94Oxe2x80x94C linkages resulting from reaction of phenolic hydroxyl groups therein with an alkenyl ether compound or halogenated alkyl ether compound, and the amount of the acid labile group and the crosslinking-group combined is on the average from more than 0 mol % to 80 mol % of the entirety of hydrogen atoms in the phenolic hydroxyl groups in formula (9) wherein e=0, f=0 and g=1.
The resist composition may further include one or more of the following components: (E) a dissolution regulator, (F) a basic compound, (G) an aromatic compound having a group:=xe2x95x90Cxe2x80x94COOH in a molecule, (H) a UV absorber, and (I) an acetylene alcohol derivative.
In a third aspect, the invention provides a process for forming a resist pattern comprising the steps of:
(i) applying a chemically amplified positive resist composition as set forth above onto a substrate,
(ii) heat treating the coated film and then exposing it to actinic radiation having a wavelength of up to 300 nm or electron beams through a photo mask, and
(iii) optionally heat treating the exposed film and developing it with a developer.
The polymer of the invention is characterized by the terminal modification of polyhydroxystyrene derivatives. When the terminally modified polymer is blended as the base resin in a chemically amplification type positive resist composition, the properties of the composition are improved over conventional base resins owing to the effects of the end groups of the polymer. For example, termination of the polymer with carboxylic acid leads to an improvement in environmental stability. By terminating with alcohol, the polymer becomes hydrophilic and improved in adhesion to the substrate. Additionally, the dissolution rate of over-exposed areas is increased over conventional base resins, leading to a further increase of alkali dissolution rate contrast before and after exposure.
Like side chains, end groups of the polymer may be crosslinked with crosslinking groups having Cxe2x80x94Oxe2x80x94C linkages. When terminals of polyhydroxystyrene are crosslinked, there results linear crosslinking, which contributes to a further increase in the dissolution rate of over-exposed areas over conventional base resins, leading to a yet further increase of alkali dissolution rate contrast before and after exposure.
More particularly, in the case of a polymer in which alkoxyalkyl groups alone have been added to the phenolic hydroxyl groups on side chains, a T-top profile does not readily arise because the elimination reaction proceeds in weak acid. However, since the polymer is very sensitive to acids as noted above, the pattern profile narrows dramatically with the lapse of time between exposure and heat treatment. Moreover, because of low alkali dissolution inhibiting effects, a highly substituted polymer must be used to achieve an acceptable dissolution contrast, but this results in a poor thermal stability. On the other hand, when a polymer in which phenolic hydroxyl groups on side chains are protected with tert-butoxycarbonyl groups is included in the resist composition, the alkali dissolution inhibiting effects improve, as a result of which dissolution contrast is achieved at a low substitution ratio and the thermal stability is good. However, deprotection to render the polymer alkali soluble requires a photoacid generator which generates a strong acid such as trifluoromethane-sulfonic acid. Unfortunately, the use of such a strong acid tends to result in the T-top profile mentioned earlier.
As opposed to the above-described two types of polymers, a polymer which is terminally modified and optionally, crosslinked within a molecule and/or between molecules with crosslinking groups having Cxe2x80x94Oxe2x80x94C linkages and resulting from the reaction of at least one of the phenolic hydroxyl groups in the polymer, the hydroxyl groups represented by R5 in formula (2), and the hydroxyl groups in formula (3) with an alkenyl ether compound or a halogenated alkyl ether compound provides a solution to both the low heat resistance of the polymers having side chains protected with acetal groups as well as the tendency of the polymers protected with tert-butoxycarbonyl groups to form a T-top profile.
The polymer used in the chemically amplified positive resist composition according to the invention has further advantages. When the inventive polymer is crosslinked with a crosslinking group having an acid labile Cxe2x80x94Oxe2x80x94C linkage and protected with an acid labile group, unexposed areas of a resist film remain unchanged with respect to weight average molecular weight and solubility in alkaline developer whereas the weight average molecular weight of exposed areas is restored to the weight average molecular weight of alkali soluble base resin prior to the protection with the crosslinking and acid labile groups, through cleavage by the generated acid and further through elimination of the acid labile group. Then the rate of alkali dissolution in the exposed areas is significantly increased as compared with the unexposed areas, resulting in an increased dissolution contrast. As a consequence, high resolution is achieved. Especially when the polymer is crosslinked at terminals, the dissolution rate of over-exposed areas is increased, leading to a further increase of alkali dissolution rate contrast before and after exposure.
When the crosslinking groups having Cxe2x80x94Oxe2x80x94C linkages are cleaved by the acid, alcohol compounds (including diol, triol and polyol compounds) are formed. The hydrophilic groups of the alcohol compounds increase the affinity of the resist to the alkali developer, which also helps to achieve a higher resolution.
Further, on the design of a resist composition, a variety of polymers having a varying alkali dissolution rate are required so as to comply with the type and amount of a particular photoacid generator and additive. It is also required to prepare such polymers in a reproducible manner. The use of the inventive polymer allows a freedom of design by eliminating the limit on the selection of an acid labile group and crosslinking group and the limit on a degree of substitution.
More specifically, a chemically amplified positive resist composition using the inventive polymer as a base resin minimizes the problems of T-top profile forming tendency, pattern configuration thinning and low heat resistance found in the prior art and increases the dissolution contrast of a resist film. As a consequence, the chemically amplified positive resist composition has high sensitivity, high resolution, allows the size and configuration of a pattern to be controlled in terms of composition, and offers improved process adaptability and reproducibility.
Polymer
The novel polymer of the present invention is a high molecular weight compound which has at least one type of acid labile group, modified at terminals, and has a weight average molecular weight of 1,000 to 500,000. It may be crosslinked within a molecule and/or between molecules with a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage.
The styrene polymer of the invention has recurring units of the following general formula (1xe2x88x92i) and is terminated with P. That is, the polymer is represented by the following general formula (1). 
In the formulas, R is hydroxyl or OR3 groups, at least one of R groups being hydroxyl, R1 is hydrogen or methyl, R2 is a normal, branched or cyclic alkyl group of 1 to 30 carbon atoms, R3 is an acid labile group, letter x is 0 or a positive integer, y is a positive integer, satisfying x+yxe2x89xa65, k is 0 or a positive integer, m is 0 or a positive integer, n is a positive integer, satisfying k+m+nxe2x89xa65, p and q are positive numbers satisfying 0 less than q xe2x89xa60.8 and p+q=1, with the proviso that the R3 groups may be the same or different when n is at least 2, xcex94 is such a number that the polymer may have a weight average molecular weight of 1,000 to 500,000, and P is hydrogen, normal, branched or cyclic alkyl or alkenyl groups of 1 to 30 carbon atoms, aromatic hydrocarbon groups of 6 to 50 carbon atoms, carboxyl, hydroxyl, or groups of the following general formula (2), (3) or (4), with the proviso that all the end groups are not hydrogen at the same time. 
In the formulas, R4(r+1)-valence aliphatic hydrocarbon groups or alicyclic saturated hydrocarbon groups of 1 to 30 carbon atoms, or aromatic hydrocarbon groups of 6 to 50 carbon atoms, R5 is normal, branched or cyclic alkyl groups of 1 to 30 carbon atoms, aromatic hydrocarbon groups of 6 to 50 carbon atoms, alkoxy groups of 1 to 30 carbon atoms, or hydroxyl, R5a is normal, branched or cyclic alkyl groups of 1 to 30 carbon atoms or aromatic hydrocarbon groups of 6 to 50 carbon atoms, letter h is 0 or 1, and letter r is a positive integer of 1 to 3.
The polymer of formula (1) may be crosslinked within a molecule and/or between molecules with a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage resulting from reaction of at least one of the phenolic hydroxyl groups represented by R in formula (1), the hydroxyl groups represented by R5 in formula (2), and the hydroxyl groups in formula (3) with an alkenyl ether compound or halogenated alkyl ether compound. The amount of the acid labile group and the crosslinking group combined is on the average from more than 0 mol % to 80 mol % of the entirety of hydrogen atoms in the phenolic hydroxyl groups in formula (1), the hydroxyl groups represented by RS in formula (2), and the hydroxyl groups in formula (3).
In formula (1), R is hydroxyl or OR3 groups, and at least one R group is hydroxyl. R1 is hydrogen or methyl. R2 represents normal, branched or cyclic alkyl groups of 1 to 30 carbon atoms, preferably 1 to 15 carbon atoms, more preferably 1 to 8 carbon atoms. Examples of the normal, branched or cyclic alkyl group include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, cyclohexyl and cyclopentyl. R3 is an acid labile group. Letter x is 0 or a positive integer, y is a positive integer, satisfying x+y xe2x89xa65. Preferably, y is 1 to 3, more preferably 1 or 2. Letter k is 0 or a positive integer, m is 0 or a positive integer, n is a positive integer, satisfying k+m+nxe2x89xa65. Preferably, n is 1 or 2 and m is 0 or 1. The R3 groups may be the same or different when n is 2 or more. Letters p and q are positive numbers satisfying 0 less than qxe2x89xa60.8 and p+q=1.
P is hydrogen, normal, branched or cyclic alkyl or alkenyl groups of 1 to 30 carbon atoms, preferably 1 to 15 carbon atoms, more preferably 1 to 8 carbon atoms, aromatic hydrocarbon groups of 6 to 50 carbon atoms, preferably 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, carboxyl, hydroxyl, or groups of the general formula (2), (3) or (4), with the proviso that all the end groups P are not hydrogen at the same time.
Examples of the normal, branched or cyclic alkyl or alkenyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, octyl, nonanyl, decyl, undecyl, dodecyl, tridecyl, pentadecyl, heptadecyl, nonadecyl, docosanyl, heptacosanyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 2,2,3-trimethylbutyl, hexamethylethyl, decahydronaphthyl, cyclohexyl, dicyclohexyl, norbornyl, norpinyl, adamantyl, 1,3-dimethyladamantyl, cyclopentyl, vinyl, allyl, butenyl, hexenyl, and cyclohexenyl.
Examples of the aromatic hydrocarbon groups include phenyl, benzyl, tert-butylbenzyl, diphenyl, triphenyl, naphthyl, anthranyl, 1,2,3-tripentylbenzyl, and hexapentylbenzyl.
Examples of the (r+1)-valence aliphatic hydrocarbon groups or alicyclic saturated hydrocarbon groups represented by R4 in formulas (2) to (4) include methylene, ethylene, n-propylene,-isopropylene)-n-butylene, isobutylene, sec-butylene, tert-butylene, pentylene, hexylene, octylene, nonanylene, decylene, undecylene, dodecylene, tridecylene, pentadecylene, heptadecylene, nonadecylene, docosanylene, heptacosanylene, 2,2-dimethylbutylene, 2,3-dimethylbutylene, 2,2,3-trimethylbutylene, hexamethylethylene, decahydro-napthalene, cyclohexavinylene, cyclohexylene, cyclohexeylene, dicyclohexylene, norbornylene, adamantylene, 1,3-dimethyladamantylene, cyclopentylene, and trivalent and tetravalent groups obtained by further eliminating one or two hydrogen atoms from the foregoing groups.
Examples of the (r+1)-valence aromatic hydrocarbon groups represented by R4 include phenylene, benzylene, tert-butylbenzylene, diphenylene, triphenylene, naphthylene, anthranylene, 1,2,3-tripentylbenzylene, hexapentylbenzylene, and trivalent and tetravalent groups obtained by further eliminating one or two hydrogen atoms from the foregoing groups.
Examples of the normal, branched or cyclic alkyl groups and aromatic hydrocarbon groups represented by R5 are the same as described above. Examples of the alkoxy groups represented by R5 include methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy, hexyloxy, octyloxy, nonanyloxy, decyloxy, undecyloxy, dodecyloxy, tridecyloxy, pentadecyloxy, heptadecyloxy, nonadecyloxy, docosanyloxy, heptacosanyloxy, 2,2-dimethylbutoxy, 2,3-dimethylbutoxy, 2,2,3-trimethylbutoxy, hexamethylethoxy, cyclohexyloxy, decahydronaphthyloxy, dicyclohexyloxy, norbornyloxy, norpinyloxy, adamantyloxy, 1,3-dimethyladamantyloxy, and cyclopentyloxy.
The acid labile group represented by R3 may be selected from a variety of acid labile groups, preferably from groups of the following formulas (7) and (8), tert-alkyl groups of 4 to 20 carbon atoms, trialkylsilyl groups whose alkyl groups each have 1 to 6 carbon atoms, and oxoalkyl groups of 4 to 20 carbon atoms. 
In formulas (7) and (8), R9 and R10 each are hydrogen or a normal, branched or cyclic alkyl group having 1 to 8 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 5 carbon atoms. R11 is a monovalent hydrocarbon group of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, which may have a hetero atom such as oxygen. Alternatively, R9 and R10, R9 and R11, or R10 and R11, taken together, may form a ring, with the proviso that R9, R10 and R11 each are a normal or branched alkylene group having 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, when they form a ring. R12 is a tertiary alkyl group having 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms, more preferably 4 to 10 carbon atoms, a trialkylsilyl group whose alkyl groups each have 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms, more preferably 4 to 10 carbon atoms, or a group of formula (6). Letter A is an integer of 0 to 6.
Examples of the normal, branched or cyclic alkyl group of 1 to 8 carbon atoms represented by R9 and R10 are as described for R2.
Examples of the hydrocarbon group represented by R11 include normal, branched or cyclic alkyl groups, substituted or unsubstituted aryl groups such as phenyl, p-methylphenyl, p-ethylphenyl, and alkoxyphenyl groups (e.g., p-methoxyphenyl), and aralkyl groups such as benzyl and phenethyl, as well as modified ones of these groups, for example, alkyl groups in which an oxygen atom intervenes, the hydrogen atom attached to a carbon atom is replaced by a hydroxyl group, or two hydrogen atoms are replaced by an oxygen atom to form a carbonyl group, as shown below.
xe2x80x94(CH2)4OH 
xe2x80x94(CH2)2O(CH2)3CH3 

xe2x80x94(CH2)2O(CH2)2OH 
xe2x80x94(CH2)6OH 

Examples of the tertiary alkyl group represented by R12 include tert-butyl, 1-methylcyclohexyl, 2-(2-methyl)-adamantyl and tert-amyl groups.
Examples of the trialkylsilyl group represented by R12 include those wherein alkyl moieties each have 1 to 6 carbon atoms such as trimethylsilyl, triethylsilyl and dimethyl-tert-butylsilyl groups. Examples of the oxoalkyl group represented by R12 include 3-oxocyclohexyl and groups of the following formulas. 
Examples of the acid labile group of formula (7) include normal or branched acetal groups such as 1-methoxyethyl, 1-ethoxyethyl, 1-n-propoxyethyl, 1-iso-propoxyethyl, 1-n-butoxyethyl, 1-iso-butoxyethyl, 1-sec-butoxyethyl, 1-tert-butoxyethyl, 1-tert-amyloxyethyl, 1-ethoxy-n-propyl, 1-cyclohexyloxyethyl, methoxypropyl, ethoxypropyl, 1-methoxy-1-methylethyl, and 1-ethoxy-1-methylethyl; and cyclic acetal groups such as tetrahydro-furanyl and tetrahydropyranyl, with the ethoxyethyl, butoxyethyl and ethoxypropyl groups being preferred. Examples of the acid labile group of formula (8) include tert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl, tert-amyloxycarbonylmethyl, 1-ethoxy-ethyoxycarbonylmethyl, 2-tetrahydropyranyloxy-carbonylmethyl, and 2-tetrahydrofuranyloxycarbonylmethyl groups.
In the invention, the P-terminated polymer of formula (1) may be crosslinked within a molecule and/or between molecules with crosslinking groups having Cxe2x80x94Oxe2x80x94C linkages resulting from reaction of one or more of the phenolic hydroxyl groups represented by R in formula (1), the hydroxyl groups represented by R5 in formula (2), and the hydroxyl groups in formula (3) with an alkenyl ether compound or halogenated alkyl ether compound to be described later. The amount of the acid labile groups and the crosslinking groups combined is on the average from more than 0 mol % to 80 mol % of the entirety of hydrogen atoms in the phenolic hydroxyl groups in formula (1), the hydroxyl groups represented by R5 in formula (2), and the hydroxyl groups in formula (3).
The crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage is exemplified by groups of the following general formulas (6a) and (6b), preferably formulas (6axe2x80x2) and (6bxe2x80x2). 
Herein, R6 and R7 each are hydrogen or a normal, branched or cyclic alkyl group of 1 to 8 carbon atoms, or R6 and R7, taken together, may form a ring, with the proviso that each of R6 and R7 is a normal or branched alkylene group of 1 to 8 carbon atoms when they form a ring. R8 is a normal, branched or cyclic alkylene group of 1 to 10 carbon atoms. Letter d is 0 or an integer of 1 to 10. A is a c-valent aliphatic or alicyclic saturated hydrocarbon group, aromatic hydrocarbon group or heterocyclic group of 1 to 50 carbon atoms, which may have an intervening hetero atom and in which the hydrogen atom attached to a carbon atom may be partially replaced by a hydroxyl group, carboxyl group, acyl group or halogen atom. B is xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94NHCOxe2x80x94Oxe2x80x94 or xe2x80x94NHCONHxe2x80x94. Letter c is an integer of 2 to 8, and cxe2x80x2 is an integer of 1 to 7. 
Herein, R6 and R7 each are hydrogen or a normal, branched or cyclic alkyl group of 1 to 8 carbon atoms, or R6 and R7, taken together, may form a ring, with the proviso that each of R6 and R7 is a normal or branched alkylene group of 1 to 8 carbon atoms when they form a ring. R8 is a normal, branched or cyclic alkylene group of 1 to 10 carbon atoms. Letter d is 0 or an integer of 1 to 5. A is a cxe2x80x3-valent normal, branched or cyclic alkylene, alkyltriyl or alkyltetrayl group of 1 to 20 carbon atoms or an arylene group of 6 to 30 carbon atoms, which may have an intervening hetero atom and in which the hydrogen atom attached to a carbon atom may be partially replaced by a hydroxyl group, carboxyl group, acyl group or halogen atom such as fluorine atom. B is xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94NHCOxe2x80x94Oxe2x80x94 or xe2x80x94NHCONHxe2x80x94. Letter cxe2x80x2 is an integer of 2 to 4, and cxe2x80x3xe2x80x2 is an integer of 1 to 3.
The normal, branched or cyclic alkyl groups of 1 to 8 carbon atoms are as exemplified above. Examples of the group represented by A are described later. These crosslinking groups of formulas (6a) and (6b) originate from alkenyl ether compounds and halogenated alkyl ether compounds to be described later.
As understood from the value of cxe2x80x2 in formula (6a) or (6b), the crosslinking group is not limited to a divalent one and trivalent to octavalent groups are acceptable. For example, the divalent crosslinking group is exemplified by groups of the following formulas (6axe2x80x2) and (6bxe2x80x2) and the trivalent crosslinking group is exemplified by groups of the following formulas (6axe2x80x3xe2x80x2) and (6bxe2x80x3xe2x80x2). 
More specifically, the polymer according to the invention is a polymer of the following general formula (5) having recurring units of the following general formula (5-i) and terminated with P, especially a crosslinked polymer of the following general formula (5) having recurring units of the following general formula (5-i) and terminated with P, which polymer is crosslinked within a molecule and/or between molecules through the mechanism that hydrogen atoms are eliminated from phenolic hydroxyl groups represented by R and/or the hydroxyl groups represented by R5 in formula (2) and/or the hydroxyl groups in formula (3) to leave oxygen atoms which are connected by a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage of the general formula (6a) or (6b). 
In the formulas, R represents hydroxyl or OR3 groups, and at least one R group is hydroxyl. R1 is hydrogen or methyl. R2 is a normal, branched or cyclic alkyl group of 1 to 30 carbon atoms. R3 is an acid labile group. R9 and R10 are hydrogen or normal, branched or cyclic alkyl groups of 1 to 8 carbon atoms. R11 is a monovalent hydrocarbon group of 1 to 18 carbon atoms which may have a hetero atom. Alternatively, R9 and R10, R9 and R11, and R10 and R11, taken together, may form a ring, and each of R9, R10 and R11 is a normal or branched alkylene group of 1 to 18 carbon atoms when they form a ring. R12 is a tertiary alkyl group of 4 to 20 carbon atoms, a trialkylsilyl group whose alkyl groups each have 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group represented by xe2x80x94CR9R10OR11. Letter a is an integer of 0 to 6. Letters p1 and p2 are positive numbers, q1 and q2 are 0 or positive numbers, satisfying 0 less than p1/(p1+q1+p2+q2)xe2x89xa60.8, 0xe2x89xa6q1/(p1+q1+p2+q2)xe2x89xa60.8, 0xe2x89xa6q2/(p1+q1+p2+q2)xe2x89xa60.8, and p1+q1+p2+q2=1, q1 and q2 are not equal to 0 at the same time; x, y, k, m, n, xcex94, and P are as defined above; and p1+p2=p and q1+q2=q.
Illustrative examples and preferred ranges for R, R1 to R3, R9 to R12, x, y, k, m, n, a, and P here are the same as those mentioned above.
Letters p1 and p2 are positive numbers and q1 and q2 are 0 or positive numbers, satisfying 0 less than p1/(p1+q1+q2+p2)xe2x89xa60.8, 0xe2x89xa6q1/(p1+q1+q2+p2)xe2x89xa60.8, 0xe2x89xa6q2/(p1+q1+q2+p2)xe2x89xa6=0.8, and p1+q1+q2+p2=1, provided that q1 and q2 are not both 0. Preferred values for p1, p2, q1, and q2 are given below.
0 less than p1/(p1+q1+p2+q2)xe2x89xa60.4, especially 0.002xe2x89xa6p1/(p1+q1+p2+q2)xe2x89xa60.2 
0xe2x89xa6q1/(p1+q1+p2+q2)xe2x89xa60.6, especially 0xe2x89xa6q1/(p1+q1+p2+q2)xe2x89xa60.4 
0xe2x89xa6q2/(p1+q1+p2+q2)xe2x89xa60.6, especially 0xe2x89xa6q2/(p1+q1+p2+q2)xe2x89xa60.4 0.4xe2x89xa6p2/(p1+q1+p2+q2) less than 1, especially 0.5xe2x89xa6p2/(p1+q1+p2+q2)xe2x89xa60.9 
0xe2x89xa6(q1+q2)/(p1+q1+p2+q2) less than 0.6, especially 0.1xe2x89xa6(q1+q2)/(p1+q1+p2+q2)xe2x89xa60.4 
Also, q1/(q1+q2) is preferably 0 to 1, more preferably 0.5 to 1, and most preferably 0.7 to 1.
Also in this polymer, the amount of the acid labile groups and the crosslinking groups combined is on the average from more than 0 mol % to 80 mol % of the entirety of hydrogen atoms in the phenolic hydroxyl groups in formula (5), the hydroxyl groups represented by R5 in formula (2), and the hydroxyl groups in formula (3).
Illustrative examples of the polymer include the polymers having recurring units of the following formulas (5xe2x80x2-1) to (5xe2x80x2-7) and terminated with P. 
In the above formulas, h is equal to 0 or 1, y is an integer of 1 to 3, U1, U2, and U3 represents the following units. 
Also herein, P is hydrogen, normal, branched or cyclic alkyl or alkenyl groups of 1 to 30 carbon atoms, aromatic hydrocarbon groups of 6 to 50 carbon atoms, carboxyl, hydroxyl, or groups of general formula (2), (3) or (4), and all the end groups P are not hydrogen at the same time. Q is a crosslinking group having a xe2x80x94Cxe2x80x94Oxe2x80x94C linkage, typically a crosslinking group of formula (6a) or (6b) above, especially a crosslinking group of formula (6axe2x80x3), (6bxe2x80x3), (6axe2x80x3xe2x80x2), or (6bxe2x80x3xe2x80x2). In cases where the crosslinking group has a valence of 3 or more, Q in above formula (5) is attached to three or more of the following units. 
It is noted that formulas (5xe2x80x2-2) and (5xe2x80x2-5) show an intramolecular linkage and the remaining formulas show an intermolecular linkage. They may be present alone or in admixture.
In the crosslinked embodiment of the present invention, the polymer is crosslinked within a molecule and/or between molecules with a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage resulting from reaction of some of the phenolic hydroxyl groups therein and/or the hydroxyl groups represented by R5 in formula (2) and/or the hydroxyl groups in formula (3) with an alkenyl ether compound or halogenated alkyl ether compound. It is preferred herein that the amount of the acid labile groups and the crosslinking groups combined be on the average from more than 0 mol % to 80 mol %, especially 2 to 50 mol %, of the entirety of hydrogen atoms in the phenolic hydroxyl groups in formula (1) and/or the hydroxyl groups represented by R5 in formula (2) and/or the hydroxyl groups in formula (3).
In this regard, the average proportion of the crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage is from more than 0 mol % to 80 mol %, especially from 0.2 to 20 mol % of the entirety of hydrogen atoms in the hydroxyl groups. With 0 mol %, no benefits of the crosslinking group are obtained, resulting in a reduced contrast of alkali dissolution rate and low resolution. With more than 80 mol %, a too much crosslinked polymer will gel, become insoluble in alkali, induce a film thickness change, internal stresses or bubbles upon alkali development, and lose adhesion to the substrate due to less hydrophilic groups.
The average proportion of the acid labile group is from more than 0 mol % to 80 mol %, especially from 10 to 50 mol % of the entirety of hydrogen atoms in the hydroxyl groups. With 0 mol %, no benefits of the acid labile group are obtained, resulting in a reduced contrast of alkali dissolution rate and low resolution. With more than 80 mol %, alkali solubility will be lost and the affinity to an alkaline developer becomes low, resulting in low resolution.
By properly selecting the amounts of the crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage and the acid labile group within the above-defined ranges, the size and configuration of a resist pattern can be controlled as desired. In the polymer according to the invention, the contents of the crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage and the acid labile group have substantial influence on the dissolution rate contrast of a resist film and govern the properties of a resist composition relating to the size and configuration of a resist pattern.
The polymer of the invention should have a weight average molecular weight of 1,000 to 500,000, preferably 3,000 to 50,000. With a weight average molecular weight of less than 1,000, resists would be less resistant to heat. With a weight average molecular weight of more than 500,000, alkali solubility and resolution lowers.
It is understood that prior to crosslinking, a polymer having a wide molecular weight dispersity (Mw/Mn) contains more polymers of low molecular weight and high molecular weight. Such a wide dispersity obstructs the design of the number of crosslinks and it is rather difficult to produce resist materials having the same properties. The influence of a molecular weight and its dispersity becomes greater as the pattern rule becomes finer. In order that a resist material be advantageously used in patterning features to a finer size, the polymer should preferably be a monodisperse one having a molecular weight dispersity of 1.0 to 1.5, especially 1.0 to 1.3. However, the invention is not limited thereto, and it is, of course, acceptable to use a polymer having a dispersity of more than 1.5.
Next, the method for preparing the polymer of the invention is described.
The crosslinked polymer according to the preferred embodiment of the invention may be prepared in various ways, for example, by a method of introducing acid labile groups of formula (7) into phenolic hydroxyl groups of a polymer having recurring units of formula (1-i), isolating the polymer, and reacting it with an alkenyl ether compound or halogenated alkyl ether compound whereby the polymer is crosslinked within a molecule and/or between molecules with a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage; a method of reacting the starting polymer with an alkenyl ether compound or halogenated alkyl ether compound whereby the polymer is crosslinked within a molecule and/or between molecules with a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage, isolating the polymer, and introducing acid labile groups of formula (7) therein; or a method of carrying out reaction with an alkenyl ether compound or halogenated alkyl ether compound and introduction of acid labile groups of formula (7) together. The last-mentioned combination method is preferred. It is possible to further introduce into the thus obtained polymer acid labile groups of formula (8), tert-alkyl, trialkylsilyl or oxoalkyl groups, if necessary.
In order that the polymer having recurring units of formula (1-i) be modified at terminals with hydrogen, normal, branched or cyclic alkyl or alkenyl groups of 1 to 30 carbon atoms, aromatic hydrocarbon groups of 6 to 50 carbon atoms, carboxyl, hydroxyl, or groups of formula (2), (3) or (4), synthesis is carried out while changing conventional stoppers used in living anion polymerization into various specific stoppers. For example, when the terminals of a polymer are hydrogen atoms, water or alcohols may be used as the stopper. When the terminals are normal, branched or cyclic alkyl or alkenyl groups of 1 to 30 carbon atoms, alkyl halides such as methyl iodide, ethyl bromide and butyl bromide may be used as the stopper. When the terminals are aromatic hydrocarbon groups, halogenated aromatic hydrocarbon groups such as 4-chlorobenzene, chlorobenzyl, 4-naphthalene bromide, 4-chlorobiphenyl, and anthracene bromide may be used as the stopper. When the terminals of a polymer are carboxyl groups, carbonic acid or the like may be used as the stopper. In the case of hydroxyl groups, a combination of trimethoxyboron and hydrogen peroxide may be used.
When the terminals of a polymer are groups of formula (2), the stopper is selected from, for example, methyl-carbonyl chloride, methoxycarbonyl chloride, ethoxycarbonyl cholride, butoxycarbonyl chloride, cyclopropanecarbonyl chloride, 1-adamantanecarbonyl chloride, cyclohexanecarbonyl chloride, benzyloxycarbonyl chloride, methylcarbonylmethyl chloride, methoxycarbonyl-ethyl chloride, tert-butoxycarbonylmethyl chloride, butoxycarbonylbenzyl chloride, cyclohexyloxycarbonyl chloride, cyclopentanecarbonyl chloride, cyclopentane-carbonylemthyl chloride, 1-adamantanecarbonylhexyl chloride, cyclohexanecarbonylmethyl chloride, and benzyloxycarbonyl chloride.
When the terminals of a polymer are groups of formula (3), the stopper is selected from, for example, ethylene oxide, propylene oxide, styrene oxide, chloromethylvinylether, 2-bromoethylvinylether, 2-chloroethylvinylether, methyl ethyl ketone, cyclohexanone, pentanone, 3-acetylnoradamantane, formaldehyde, acetaldehyde, trimethylaldehyde, methyl formate, and methyl acetate.
When the terminals of a polymer are groups of formula (4), the stopper is selected from, for example, chloromethyl methyl ether, 2-bromoethyl methyl ether, chloromethyl octyl ether, chloromethyl cyclohexyl ether, and chloromethyl benzyl ether.
In these cases, the amount of the stopper added is preferably at least equimolar to the initiator.
Now, the methods of preparing the crosslinked polymers of the invention are described. Included are a first method using a polymer comprising recurring units of formula (1xe2x80x2) and terminated with P, an alkenyl ether compound of formula (I) or (II), and a compound of formula (7a) and a second method using a polymer comprising recurring units of formula (1xe2x80x2) and terminated with P, a halogenated alkyl ether compound of formula (VI) or (VII), and a compound of formula (7b).
First Method 
Here, R1, R2 R8, R9, x, y, p1, p2, q1, and q2 are as defined above, and p1+p2+q1+q2=1. R5 and R6 are as defined above, R9a and R6a each are hydrogen or a normal, branched or cyclic alkyl group of 1 to 7 carbon atoms.
In formula (I) or (II) representing the vinyl ether compound, A is a c-valent aliphatic saturated hydrocarbon, alicyclic saturated hydrocarbon, aromatic hydrocarbon or heterocyclic group having 1 to 50 carbon atoms, which may contain an intervening hetero atom, and in which some of the hydrogen atoms attached to the carbon atoms may be substituted with hydroxyl, carboxyl, acyl, or fluorine. B is xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94NHCOxe2x80x94Oxe2x80x94 or xe2x80x94NHCONHxe2x80x94. Letter c is an integer of 2 to 8, and d is 0 or an integer of 1 to 10.
The c-valent (divalent to octavalent) hydrocarbon groups represented by A include hydrocarbon groups, for example, substituted or unsubstituted alkylene groups having 1 to 50 carbon atoms, especially 1 to 40 carbon atoms, substituted or unsubstituted arylene groups having 6 to 50 carbon atoms, especially 6 to 40 carbon atoms, a combination of an alkylene group and an arylene group, and cxe2x80x3-valent groups obtained by eliminating one hydrogen atom attached to a carbon atom from the foregoing groups wherein cxe2x80x2 is an integer of 3 to 8; and c-valent heterocyclic groups, and a combination of such a heterocyclic group with any one of the foregoing hydrocarbon groups. In the alkylene and arylene groups, a hetero atom such as O, NH, N(CH3), S and SO2 may intervene and where substituted, the substituent is a hydroxyl, carboxyl, acyl group or fluorine atom.
Illustrative examples of A are given below. 
A method such as that described by Stephen C. Lapin in Polymers Paint Colour Journal, 179 (4237), 321 (1988) may be used to prepare the compounds of general formula (I). This method involves synthesis via the reaction of a polyhydric alcohol or a polyhydric phenol with acetylene, or the reaction of a polyhydric alcohol or polyhydric phenol with a halogenated alkyl vinyl ether.
Illustrative, non-limiting examples of compounds having formula (I) include ethylene glycol divinyl ether, triethylene glycol divinyl ether, 1,2-propanediol divinyl ether, 1,3-propanediol divinyl ether, 1,3-butanediol divinyl ether, 1,4-butanediol divinyl ether (tetramethylene glycol divinyl ether), neopentyl glycol divinyl ether, trimethylolpropane trivinyl ether, trimethylolethane trivinyl ether, hexanediol divinyl ether, 1,4-cyclohexanediol divinyl ether, 1,4-divinyloxymethyl cyclohexane, tetraethylene glycol divinyl ether, pentaerythritol divinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitol pentavinyl ether, ethylene glycol diethylene vinyl ether, triethylene glycol diethylene vinyl ether, ethylene glycol dipropylene vinyl ether, triethylene glycol diethylene vinyl ether, trimethylolpropane triethylene vinyl ether, trimethylol-propane diethylene vinyl ether, pentaerythritol diethylene vinyl ether, pentaerythritol triethylene vinyl ether, pentaerythritol tetraethylene vinyl ether, and compounds of-the formulas (I-1) to (I-31) given below. 
When B is xe2x80x94COxe2x80x94O, the compound of general formula (II) above may be prepared by reacting a polycarboxylic acid with a halogenated alkyl vinyl ether. Illustrative, non-limiting examples of compounds having formula (II) in which B is xe2x80x94COxe2x80x94Oxe2x80x94 include diethylene vinyl ether terephthalate, diethylene vinyl ether phthalate, diethylene vinyl ether isophthalate, dipropylene vinyl ether phthalate, dipropylene vinyl ether terephthalate, dipropylene vinyl ether isophthalate, diethylene vinyl ether maleate, diethylene vinyl ether fumarate, and diethylene vinyl ether itaconate.
Examples of alkenyl ether group-containing compounds which are highly suitable for use in the invention include alkenyl ether group-containing compounds prepared by reacting an active hydrogen-bearing alkenyl ether compound of general formula (III), (IV), or (V) below, for example, with an isocyanate group-bearing compound. 
In these formulas, R6a, R7, and R8 are as defined above.
When B is xe2x80x94NHCOxe2x80x94Oxe2x80x94 or xe2x80x94NHCONHxe2x80x94, the compound of general formula (II) above can be prepared by using isocyanate group-bearing compounds including those mentioned in Handbook of Crosslinking Agents, Taisei K.K., 1981. Illustrative examples include polyisocyanate compounds such as triphenylmethane truisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, the dimer of 2,4-tolylene diisocyanate, naphthalene-1,5-diisocyanate, o-tolylene diisocyanate, polymethylene polyphenyl isocyanate, and hexamethylene diisocyanate; and polyisocyanate adducts such as the adduct of tolylene diisocyanate and trimethylolpropane, the adduct of hexamethylene diisocyanate and water, and the adduct of xylene diisocyanate and trimethylolpropane. Various compounds with terminal alkenyl ether groups may be obtained by reacting the above-mentioned isocyanate group-bearing bearing compounds with the active hydrogen-bearing alkenyl ether compounds. Illustrative, non-limiting examples of such compounds include those of the following formulas (II-1) to (II-11). 
In the first method discussed above, the hydrogen atoms on the phenolic hydroxyl groups of polymers having recurring units of general formula (1xe2x80x2), terminated with P, having a weight average molecular weight of 1,000 to 500,000 and preferably having a molecular weight distribution of 1.0 to 1.5 are reacted with p1 moles of an alkenyl ether compound of general formula (I) or (II) and q1 moles of a compound of general formula (7a), per mole of all the hydroxyl groups on the polymer, so as give polymers having recurring units of general formulas (5axe2x80x2-1) to (5axe2x80x2-7) below and terminated with P, for example. It is noted that the end groups P of the polymers may be further reacted with compounds of general formula (7a). In the formulas below, m+n=y, and h, k, m, n, x, y, p1, p2, q1, q2, R1, R2 R9, R10, R11, and Q are as defined above 
In the first method, reaction is preferably carried out in a solvent in the presence of an acid. The reaction solvent is preferably a polar aprotic solvent such as dimethylformamide, dimethylacetamide, tetrahydrofuran, or ethyl acetate. These may be used alone or as mixtures of two or more thereof. Preferable examples of the acid catalyst include hydrochloric acid, sulfuric acid, trifluoromethanesulfonic acid, p-toluenesulfonic acid, methanesulfonic acid, trifluoroacetic acid, and pyridinium p-toluenesulfonate. The amount of the acid catalyst used is preferably 0.1 to 10 mol % based on the moles of the entire phenolic hydroxyl groups of the polymer having general formula (1). The reaction temperature is xe2x88x9220 to 100xc2x0 C., and preferably-0 to 60xc2x0 C., and the reaction time is 0.2 to 100 hours, and preferably 0.5 to 20 hours.
Where two types of reaction are carried out in a contiguous manner without once isolating an intermediate product, the order of addition of the alkenyl ether compound of formula (I) or (II) and the compound of formula (7a) is not critical. Preferably, the compound of formula (7a) is first added and after reaction proceeds to a full extent, the alkenyl ether compound of formula (I) or (II) is added. If the alkenyl ether compound of formula (I) or (II) and the compound of formula (7a) are simultaneously added or if the alkenyl ether compound of formula (I) or (II) is first added, then some of reactive sites of the alkenyl ether compound of formula (I) or (II) can be hydrolyzed with water in the reaction system whereby there is formed a polymer of complex structure which is difficult to control its physical properties.
Second Method 
Here, R1, R2 R6 to R11, x, y, p1, p2, q1, q2, A, B, c, and d-are as defined above, and Z is a halogen atom such as Cl, Br or I.
It is understood that the compounds of formulas (VI), (VII) and (7b) can be produced by reacting the compounds of formulas (I), (II) and (7a) with hydrogen chloride, hydrogen bromide or hydrogen iodide, respectively.
In the second method, polymers comprising recurring units of formula (1xe2x80x2), terminated with P, and having a weight average molecular weight of 1,000 to 500,000 and preferably a dispersity of 1.0 to 1.5 are reacted with p1 moles of a halogenated alkyl ether compound of formula (VI) or (VII) and q1 moles of a compound of formula (7b) per mole of the phenolic hydroxyl group in the polymer to be reacted, thereby forming polymers having recurring units of the formulas (5axe2x80x2-1) to (5axe2x80x2-7) shown above and terminated with P. It is noted that the end groups P of the polymers may be further reacted with a compound of formula (7b).
In the second method, reaction is preferably carried out in a solvent in the presence of a base. The reaction solvent used herein is preferably selected from aprotic polar solvents such as acetonitrile, acetone, dimethyl-formamide, dimethylacetamide, tetrahydrofuran, and dimethylsulfoxide, and mixtures thereof. The base used herein is preferably selected from triethylamine, pyridine, diisopropylamine and potassium carbonate. The amount of the base used is preferably at least (p1+q1) moles per mole of the phenolic hydroxyl group in the polymer of formula (1xe2x80x2) to be reacted. Reaction is preferably carried out at a temperature of xe2x88x9250xc2x0 C. to 100xc2x0 C., more preferably 0xc2x0 C. to 60xc2x0 C. The reaction time is generally about xc2xd to 100 hours, preferably 1 to 20 hours.
It is acceptable to take a reaction sequence of first reacting a polymer having recurring units of formula (1xe2x80x2) and terminated with P with a compound of formula (7a) or (7b) to form a polymer having recurring units of the following general formula (10) and terminated with P, isolating the polymer of formula (10), and then crosslinking the polymer of formula (10) using a compound of formula (I), (II), (VI) or (VII). 
Furthermore, by introducing another acid labile group into the polymers having recurring units of formulas (5axe2x80x2-1) to (5axe2x80x2-7) and terminated with P, which are obtained by the first or second method, polymers having recurring units of formulas (5xe2x80x2-1) to (5xe2x80x2-7) and terminated with P can be produced if necessary. This is done by reacting the polymer of formula (5axe2x80x2-1) to (5axe2x80x2-7) with q2 moles of a dialkyl dicarbonate compound or alkoxycarbonylalkyl halide per mole of the phenolic hydroxyl group in the original polymer having recurring units of formula (1xe2x80x2) and terminated with P to introduce an acid labile group of the following general formula (8); or by reacting the polymer of formula (5axe2x80x2-1) to (5axe2x80x2-7) with a tert-alkyl halide, trialkylsilyl halide or oxoalkyl compound to introduce an acid labile group.
Preferably the introduction of an acid labile group of formula (8) is carried out in a solvent in the presence of a base. The reaction solvent used herein is preferably selected from aprotic polar solvents such as acetonitrile, acetone, dimethylformamide, dimethylacetamide, tetrahydro-furan, and dimethylsulfoxide, and mixtures thereof. The base used herein is preferably selected from triethylamine, pyridine, imidazole, diisopropylamine and potassium carbonate. The amount of the base used is preferably at least q2 moles per mole of the phenolic hydroxyl group in the original polymer of formula (1xe2x80x2). Reaction is preferably carried out at a temperature of 0xc2x0 C. to 100xc2x0 C., more preferably 0xc2x0 C. to 60xc2x0 C. The reaction time is generally about 10 minutes to 100 hours, preferably 1 to 10 hours.
Examples of the dialkyl dicarbonate compound include di-tert-butyl dicarbonate and di-tert-amyl dicarbonate. Examples of the alkoxycarbonylalkyl halide include tert-butoxycarbonylmethyl chloride, tert-amyloxycarbonylmethyl chloride, tert-butoxycarbonylmethyl bromide, tert-butoxycarbonylethyl chloride, ethoxyethoxycarbonylmethyl chloride, ethoxyethoxycarbonylmethyl bromide, tetrahydropyranyloxycarbonylmethyl chloride, tetrahydropyranyloxycarbonylmethyl bromide, tetrahydrofuranyloxycarbonylmethyl chloride, and tetrahydrofuranyloxycarbonylmethyl bromide. Examples of the trialkylsilyl halide include trimethylsilyl chloride, triethylsilyl chloride, and dimethyl-tert-butylsilyl chloride.
Furthermore, if necessary, the polymer having recurring units of formula (5axe2x80x2-l) to (5axe2x80x2-7) and terminated with P, which is obtained by the first or second method, can be tert-alkylated or oxoalkylated by reacting the polymer with q2 moles of a tert-alkylating compound or oxoalkyl compound per mole of the phenolic hydroxyl group in the original polymer having recurring units of formula (1xe2x80x2) and terminated with P.
Preferably this reaction is carried out in a solvent in the presence of an acid. The reaction solvent used herein is preferably selected from aprotic polar solvents such as dimethylformamide, dimethylacetamide, tetrahydrofuran, and ethyl acetate, and mixtures thereof. The acid used herein is preferably selected from hydrochloric acid, sulfuric acid, trifluoromethanesulfonic acid, p-toluenesulfonic acid, methanesulfonic acid, trifluoroacetic acid, and pyridinium p-toluenesulfonate. The amount of the acid catalyst used is preferably 0.1 to 10 mol % based on the moles of the phenolic hydroxyl groups in the original polymer having recurring units of formula (1xe2x80x2) and terminated with P, the hydroxyl groups represented by R5 in formula (2) and the hydroxyl groups in formula (3). Reaction is preferably carried out at a temperature of xe2x88x9220xc2x0 C. to 100xc2x0 C., more preferably 0xc2x0 C. to 60xc2x0 C. The reaction time is generally about 10 minutes to 100 hours, preferably xc2xd to 20 hours.
Examples of the tert-alkylating compound include iso-butene, 2-methyl-1-butene, and 2-methyl-2-butene. Examples of the oxoalkyl compound include xcex1-angelica lactone, 2-cyclohexen-1-one, and 5,6-dihydro-2H-pyran-2-one.
Apart from the route of once forming a polymer of formula (5axe2x80x2-1) to (5axe2x80x27), it is possible to directly introduce an acid labile group of formula (8), tertiary alkyl group, trialkylsilyl group or oxoalkyl group into a polymer comprising recurring units of the following general formula (5bxe2x80x2-1) to (5bxe2x80x2-7) and terminated with P, and optionally further introduce an acid labile group of formula (7). 
In these formulas, R1, R2, Q, p1, p2, q1 q2, h, x, and y are each as defined above. U3xe2x80x3 represents the units shown below. 
It is possible to introduce not only one, but even two or more different acid labile groups represented by R3 into the polymer of the invention. In this case, first q1 moles of an acid labile group are introduced as described above-per mole of all the hydroxyl groups on the polymer having recurring units of formula (1xe2x80x2) and terminated with P, then q2 moles of a different acid labile group are introduced by the same method, thereby giving a polymer in which these two types of acid labile groups are introduced. By suitable repetition of this operation, a polymer in which an even greater number of types of acid labile groups are introduced can be produced.
Composition
The chemically amplified positive resist composition of the present invention uses the above-described polymer as the base resin. More particularly, the resist composition of the invention contain the following components:
(A) an organic solvent,
(B) a base resin in the form of a polymer of formula (1) above, preferably formula (5), and
(C) a photoacid generator.
In addition to above components (A) to (C), the resist composition may further include one or more of the following components (D) to (I):
(D) another base resin other than component (B) which is a polymer comprising recurring units of general formula (9): 
wherein R1, R2, R9, R10, and R11 are as defined above; R12 is an acid labile group other than xe2x80x94CR9R10OR11, letters e and f are 0 or positive numbers and g is a positive number, satisfying e+f+g=1, 0xe2x89xa6e/(e+f+g)xe2x89xa60.5, and 0.4xe2x89xa6g/(e+f+g)xe2x89xa60.9, some of the hydrogen atoms of phenolic hydroxyl groups being replaced by at least one type of acid labile group in an average proportion of 0 mol % to 80 mol % of the entirety, the polymer having a weight average molecular weight of 3,000 to 300,000, wherein the polymer of formula (9) may be crosslinked within a molecule and/or between molecules with a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage resulting from reaction of phenolic hydroxyl groups therein with an alkenyl ether compound or halogenated alkyl ether compound, and the amount of the acid labile group and the crosslinking group combined is on the average from more than 0 mol % to 80 mol % of the entirety of hydrogen atoms in the phenolic hydroxyl groups in formula (9) wherein e=0, f=0, and g=1;
(E) a dissolution regulator;
(F) a basic compound;
(G) an aromatic compound having a xe2x95x90Cxe2x80x94COOH group within the molecule;
(H) an UV absorber; and
(I) an acetylene alcohol derivative.
The organic solvent used as component (A) in the invention may be any organic solvent in which the photoacid generator, base resin, dissolution regulator, and other components are soluble. Illustrative, non-limiting, examples of the organic solvent include ketones such as cyclohexanone and methyl-2-n-amylketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; and esters such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, ethyl lactate, ethyl-pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate. These solvents may be used alone or in combinations of two or more thereof. Of the above organic solvents, preferred are diethylene glycol dimethyl ether, 1-ethoxy-2-propanol and ethyl lactate, in which the photoacid generator is most soluble, and propylene glycol monomethyl ether acetate which is safe, and mixtures thereof.
The amount of the organic solvent used is preferably about 200 to 1,000 parts, more preferably about 400 to 800 parts by weight per 100 parts by weight of the base resin consisting of components (B) and (D) combined.
Suitable examples of the photoacid generator serving as component (C) include onium salts of general formula (11) below, diazomethane derivatives of formula (12), glyoxime derivatives of formula (13), xcex2-ketosulfone derivatives, disulfone derivatives, nitrobenzylsulfonate derivatives, sulfonic acid ester derivatives, and imidoyl sulfonate derivatives.
(R30)bM+Kxe2x88x92xe2x80x83xe2x80x83(11) 
In the formula, R30 is a straight, branched or cyclic alkyl of 1 to 12 carbon atoms, an aryl of 6 to 12 carbon atoms, or an aralkyl of 7 to 12 carbon atoms; M+ is iodonium or sulfonium; Kxe2x88x92 is a non-nucleophilic counter-ion; and the letter b is 2 or 3.
Illustrative examples of alkyl groups represented by R30 include methyl, ethyl, propyl, butyl, cyclohexyl, 2-oxocyclohexyl, norbornyl, and adamantyl. Exemplary aryl groups include phenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxy-phenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; and alkylphenyl groups such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butyl-phenyl, and dimethylphenyl. Exemplary aralkyl groups include benzyl and phenethyl. Examples of the non-nucleoophilic counter-ion represented by Kxe2x88x92 include halide ions such as chloride and bromide; fluoroalkylsulfonate ions such as triflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate; arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; and alkylsulfonate ions such as mesylate and butanesulfonate. 
In the formula, R31 and R32 are straight, branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenated aryl groups of 6 to 12 carbon atoms, or aralkyl groups of 7 to 12 carbon atoms.
Illustrative examples of alkyl groups represented by R31 and R32 include methyl, ethyl, propyl, butyl, amyl, cyclopentyl, cyclohexyl, norbornyl, and adamantyl. Exemplary halogenated alkyl groups include trifluoromethyl, 1,1,1-trifluoroethyl, 1,1,1-trichloroethyl, and nonafluorobutyl. Exemplary aryl groups include phenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; and alkylphenyl groups such as 2-methyl-phenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl. Exemplary halogenated aryl groups include fluorobenzene, chlorobenzene, and 1,2,3,4,5-pentafluorobenzene. Exemplary aralkyl groups include benzyl and phenethyl. 
In the formula, R33, R34, and R35 are straight, branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenated aryl groups of 6 to 12 carbon atoms, or aralkyl groups of 7 to 12 carbon atoms. R34 and R35 may together form a cyclic structure with the proviso that if they form a cyclic structure, each is a straight or branched alkylene group of 1 to 6 carbon atoms.
The alkyl, halogenated alkyl, aryl, halogenated aryl, and aralkyl groups represented by R33, R34, and R35 are exemplified by the same groups mentioned above for R21 and R32. Examples of alkylene groups represented by R34 and R35 include methylene, ethylene, propylene, butylene, and hexylene.
Illustrative examples of the photoacid generator include:
onium salts such as diphenyliodonium trifluoro-methanesulfonate, (p-tert-butoxyphenyl)phenyliodonium trifluoromethanesulfonate, diphenyliodonium p-toluene-sulfonate, (p-tert-butoxyphenyl)phenyliodonium p-toluene-sulfonate, triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium trifluoromethane-sulfonate, bis(p-tert-butoxyphenyl)phenylsulfonium trifluoromethanesulfonate, tris(p-tert-butoxyphenyl)-sulfonium trifluoromethanesulfonate, triphenylsulfonium p-toluenesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, bis(p-tert-butoxyphenyl)phenylsulfonium p-toluenesulfonate, tris(p-tert-butoxyphenyl) sulfonium p-toluenesulfonate, triphenylsulfonium nonafluorobutanesulfonate, triphenylsulfonium butanesulfonate, trimethylsulfonium trifluoromethanesulfonate, trimethylsulfonium p-toluenesulfonate, cyclohexylmethyl(2-oxocyclohexyl)-sulfonium trifluoromethanesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium p-toluenesulfonate, dimethyl-phenylsulfonium trifluoromethanesulfonate, dimethylphenyl-sulfonium p-toluenesulfonate, dicyclohexylphenylsulfonium trifluoromethanesulfonate, and dicyclohexylphenylsulfonium p-toluenesulfonate;
diazomethane derivatives such as bis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl) diazomethane, bis(xylenesulfonyl)-diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(cyclopentylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)-diazomethane, bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazaomethane, bis(isopropylsulfonyl)-diazaomethane, bis(tert-butylsulfonyl)diazomethane, bis(n-amylsulfonyl)diazomethane, bis(isoamylsulfonyl)-diazomethane, bis(sec-amylsulfonyl)diazomethane, bis(tert-amysulfonyl)diazomethane, 1-cyclohexylsulfonyl-1-(tert-butylsulfonyl)diazomethane, 1-cyclohexylsulfonyl-1-(tert-amylsulfonyl)diazomethane, and 1-tert-amylsulfonyl-1-(tert-butylsulfonyl)diazomethane; glyoxime derivatives such as bis-o-(p-toluene-sulfonyl)-xcex1-dimethylglyoxime, bis-o-(p-toluenesulfonyl)-xcex1-diphenylglyoxime, bis-o-(p-toluenesulfonyl)-xcex1-dicyclohexylglyoxime, bis-o-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime, bis-o-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime, bis-o-(n-butanesulfonyl)-xcex1-dimethylglyoxime, bis-o-(n-butanesulfonyl)-xcex1-diphenylglyoxime, bis-o-(n-butanesulfonyl)-xcex1-dicyclohexylglyoxime, bis-o-(n-butanesulfonyl)-2,3-pentanedioneglyoxime, bis-o-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime, bis-o-(methanesulfonyl)-xcex1-dimethylglyoxime, bis-o-(trifluoromethanesulfonyl)-xcex1-dimethylglyoxime, bis-o-(1,1,1-trifluoroethanesulfonyl)-xcex1-dimethylglyoxime, bis-o-(tert-butanesulfonyl)-xcex1-dimethylglyoxime, bis-o-(perfluorooctanesulfonyl)-xcex1-dimethylglyoxime, bis-o-(cyclohexanesulfonyl)-xcex1-dimethylglyoxime, bis-o-(benzenesulfonyl)-xcex1-dimethylglyoxime, bis-o-(p-fluorobenzenesulfonyl)-xcex1-dimethylglyoxime, bis-o-(p-tert-butylbenzenesulfonyl)-xcex1-dimethylglyoxime, bis-o-(xylenesulfonyl)-xcex1-dimethyl-glyoxime, and bis-o-(camphorsulfonyl)-xcex1-dimethylglyoxime;
xcex2-ketosulfone derivatives such as 2-cyclohexyl-carbonyl -2-(p-toluenesulfonyl)propane and 2-isopropyl-carbonyl -2-(p-toluenesulfonyl)propane;
disulfone derivatives such as diphenyl disulfone and dicyclohexyl disulfone;
nitrobenzyl sulfonate derivatives such as 2,6-dinitrobenzyl p-toluenesulfonate and 2,4-dinitrobenzyl p-toluenesulfonate;
sulfonic acid ester derivatives such as 1,2,3-tris(methanesulfonyloxy)benzene, 1,2,3-tris(trifluoro-methanesulfonyloxy)benzene, and 1,2,3-tris(p-toluene-sulfonyloxy)benzene; and
imidoyl sulfonate derivatives such as phthalimidoyl triflate, phthalimidoyl tosylate, 5-norbornene-2,3-dicarboxyimidoyl triflate, 5-norbornene-2,3-dicarboxy-imidoyl tosylate, and 5-norbornene-2,3-dicarboxyimidoyl n-buylsulfonate.
Preferred among these photoacid generators are onium salts such as triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate, tris(p-tert-butoxyphenyl)sulfonium trifluoro-methanesulfonate, triphenylsulfonium p-toluenesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, and tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate; diazomethane derivatives such as bis(benzenesulfonyl)-diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(n-butylsulfonyl)-diazomethane, bis(isobutylsulfonyl)diazomethane, bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)-diazomethane, bis(isopropylsulfonyl)diazomethane, and bis(tert-butylsulfonyl)diazomethane; and glyoxime derivatives such as bis-o-(p-toluenesulfonyl)-xcex1-dimethylgloyoxime and bis-o-(n-butanesulfonyl)-xcex1-dimethylglyoxime. These photoacid generators may be used singly or in combinations of two or more thereof. Onium salts are effective for improving rectangularity, while diazomethane derivatives and glyoxime derivatives are effective for reducing standing waves. The combination of an onium salt with a diazomethane or a glyoxime derivative allows for fine adjustment of the profile.
The photoacid generator is added in an amount of 0.2 to 15 parts by weight, and especially 0.5 to 8 parts by weight, per 100 parts by weight of all the base resins. At less than 0.2 part, the amount of acid generated during exposure would be too low and the sensitivity and resolution are poor, whereas the addition of more than 15 parts would lower the transmittance of the resist and results in a poor resolution.
Component (D) is a base resin other than the polymer of component (B) described above. The other base resin is preferably a polymer having recurring units of the following general formula (9) and having a weight average molecular weight of from 3,000 to 300,000. Including component (D) is advantageous because it enables free control of the pattern dimensions and the pattern configuration. 
In this formula, R1, R2, R9, R10, and R11 are as defined above, R12 is an acid labile group other than xe2x80x94CR9R10OR11, and the letters e and f are each 0 or a positive number, and g is a positive number, satisfying e+f+g=1, 0xe2x89xa6e/(e+f+g)xe2x89xa60.5, and 0.4xe2x89xa6g/(e+f+g)xe2x89xa60.9.
The polymer of formula (9) may be crosslinked within a molecule and/or between molecules with a crosslinking group having a Cxe2x80x94Oxe2x80x94C linkage resulting from reaction of phenolic hydroxyl groups therein with an alkenyl ether compound or halogenated alkyl ether compound. The amount of the acid labile group and the crosslinking group combined is on the average from more than 0 mol % to 80 mol % of the entirety of hydrogen atoms in the phenolic hydroxyl groups in formula (9) wherein e=0, f=0, and g=1.
This polymer must have a weight average molecular weight in a range of from 3,000 to 300,000, and preferably from 5,000 to 30,000. At a weight average molecular weight of less than 3,000, the resist has a poor thermal stability, whereas above 300,000, the alkali solubility is too low to provide an acceptable resolution.
When the base resin serving as component (D) has a broad molecular weight dispersity (Mw/Mn), both low molecular weight and high molecular weight polymers are present. Too much low molecular weight polymer results in a decreased thermal stability, while too much high molecular weight polymer makes this base resin insufficiently soluble in alkali, which can lead to footing at the end of pattern formation. Therefore, given that these effects of molecular weight and molecular weight distribution tend to increase as the pattern rule becomes smaller, to obtain a resist suitable for a fine pattern rule, the base resin should preferably have a narrow molecular weight dispersity of 1.0 to 2.5, and especially 1.0 to 1.5.
The other baser resin as component (D) and the base resin as component (B) are preferably formulated in a ratio of from 0:100 to 90:10, and especially 0:100 to 50:50. When the base resin (D) is formulated in an amount greater than this weight ratio, the desirable effects of the base resin (B) (comprised of the P-terminated polymer) are not achieved.
The resist composition of the invention may also include, as component (E), a dissolution regulator for enhancing the contrast. The dissolution regulator is a compound having an average molecular weight within a range of 100 to 1,000, and preferably 150 to 800, and having on the molecule at least two phenolic hydroxyl groups, in which an average of from 0 to 100 mol % of all the hydrogen atoms on the phenolic hydroxyl groups have been replaced with acid labile groups.
The degree of substitution of the hydrogen atoms on the phenolic hydroxyl groups with acid labile groups is on average at least 0 mol %, and preferably at least 30 mol %, of all the phenolic hydroxyl groups. The upper limit is 100 mol %, and preferably 80 mol %.
Preferable examples of such compounds having two or more phenolic hydroxyl groups include those of formulas (i) to (xi) below. 
In these formulas, R21 and R22 are each hydrogen or a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms; R23 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or xe2x80x94(R27)nxe2x80x94COOH; R24 is xe2x80x94(CH2)ixe2x80x94 (where i=2 to 10), an arylene of 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R25 is an alkylene of 1 to 10 carbon atoms, an arylene of 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R26 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or a hydroxyl-substituted phenyl or naphthyl; R27 is a straight or branched alkylene of 1 to 10 carbon atoms; the letter j is an integer from 0 to 5; u and h are each 0 or 1; s, t, sxe2x80x2, txe2x80x2, sxe2x80x3, and txe2x80x3 are each numbers which satisfy s+t=8, sxe2x80x2+txe2x80x2=5, and sxe2x80x3+txe2x80x3=4, and are such that each phenyl skeleton has at least one hydroxyl group; and a is a number such that the molecular weight of the compounds of formula (viii) or (ix) is from 100 to 1,000.
In the above formulas, suitable examples of R21 and R22 include hydrogen, methyl, ethyl, butyl, propyl, ethynyl, and cyclohexyl; suitable examples of R23 include the same groups as for R21 and R22, as well as xe2x80x94COCH and xe2x80x94CH2COOH; suitable examples of R24 include ethylene, phenylene, carbonyl, sulfonyl, oxygen, and sulfur; suitable examples of R25 include methylene as well as the same groups as for R24; and suitable examples of R26 include hydrogen, methyl, ethyl, butyl, propyl, ethynyl, cyclohexyl, and hydroxyl-substituted phenyl or naphthyl.
Exemplary acid labile groups on the dissolution regulator include groups of general formula (7) or (8) above, tertiary alkyl groups of 4 to 20 carbon atoms, trialkylsilyl groups in which each of the alkyls has 1 to 6 carbon atoms, and oxoalkyl groups of 4 to 20 carbon atoms.
The compound serving here as the dissolution regulator, in which phenolic hydroxyl groups have been partially substituted with acid labile groups, may be formulated in an amount of 0 to 50 parts, preferably 5 to 50 parts, and more preferably 10 to 30 parts by weight, per 100 parts by weight of the base resin, and may be used singly or as a mixture of two or more thereof. An amount of less than 5 parts may fail to yield an improved resolution, whereas the use of more than 50 parts would lead to thinning of the patterned film, and thus a decline in resolution.
The dissolution regulators can be prepared by chemically reacting acid labile groups with a compound having phenolic hydroxyl groups in the same manner as described earlier for the base resin.
Instead of, or in addition to, the above-described dissolution regulator, the resist composition of the invention may include, as another dissolution regulator, a partially substituted compound having a weight average molecular weight of more than 1,000 and up to 3,000, and having phenolic hydroxyl groups on the molecule, in which an average of 0% to 60% of all the hydrogen atoms on the phenolic hydroxyl groups have been substituted with acid labile groups.
The compound in which the phenolic hydroxyl group hydrogens are partially substituted with these acid labile groups is preferably one or more selected from among compounds having recurring units of general formula (14) below and a weight average molecular weight of more than 1,000 and up to 3,000. 
In the formula, R3 is an acid labile group, and v and w are respectively numbers satisfying 0xe2x89xa6v/(v+w)xe2x89xa60.6.
Suitable examples of the acid labile groups in the other dissolution regulator include groups of general formula (7) or (8), tertiary alkyl groups of 4 to 20 carbon atoms, trialkylsilyl groups in which each of the alkyls has 1 to 6 carbon atoms, and oxoalkyl groups of 4 to 20 carbon atoms.
Advantageously, the other dissolution regulator just described is formulated in an amount such that the total amount of dissolution regulator, including the dissolution regulator described earlier, is 0 to 50 parts, preferably 0 to 30 parts, and more preferably at least 1 part by weight, per 100 parts by weight of the base resins.
The other dissolution regulator can be prepared by chemically reacting acid labile groups with a compound having phenolic hydroxyl groups in the same manner as described earlier for the base resin.
The basic compound used as component (F) is preferably a compound capable of suppressing the rate of diffusion when the acid generated by the photoacid generator diffuses within the resist film. The inclusion of this type of basic compound holds down the rate of acid diffusion within the resist film, resulting in better resolution. In addition, it suppresses changes in sensitivity following exposure, thus reducing substrate and environment dependence, as well as improving the exposure latitude and the pattern profile.
Examples of basic compounds suitable for use as component (F) include primary, secondary, and tertiary aliphatic amines, mixed amines, aromatic amines, heterocyclic amines, carboxyl group-bearing nitrogenous compounds, sulfonyl group-bearing nitrogenous compounds, hydroxyl group-bearing nitrogenous compounds, hydroxyphenyl group-bearing nitrogenous compounds, alcoholic nitrogenous compounds, amide derivatives, and imide derivatives. Of these, aliphatic amines are especially preferred.
Examples of suitable primary aliphatic amines include ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, iso-butylamine, sec-butylamine, pentylamine, tert-amylamine, cyclopentylamine, hexylamine, cyclohexytamine, heptylamine, octylamine, nonylamine, decylamine, dodecylamine, cetylamine, methylenediamine, ethylenediamine, and tetraethylenepentamine. Examples of suitable secondary aliphatic amines include dimethylamine, diethylamine, di-n-propylamine, di-iso-propylamine, di-n-butylamine, di-iso-butylamine, di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine, dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, didodecylamine, dicetylamine, N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, and N,N-dimethyltetraethylenepentamine. Examples of suitable tertiary aliphatic amines include trimethylamine, triethylamine, tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine, tri-iso-butylamine, tri-sec-butylamine, tripentylamine, tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, tridodecylamine, tricetylamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylmethylenediamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine, and N,N,Nxe2x80x2,Nxe2x80x2-tetramethyltetraethylenepentamine.
Examples of suitable mixed amines include dimethyl-ethylamine, methylethylpropylamine, benzylamine, phenethylamine, and benzyldimethylamine. Examples of suitable aromatic and heterocyclic amines include aniline derivatives (e.g., aniline, N-methylaniline, N-ethyl-aniline, N-propylaniline, N,N-dimethylaniline, 2-methyl-aniline, 3-methylaniline, 4-methylaniline, ethylaniline, propylaniline, trimethylaniline, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline, 2,4-dinitroaniline, 2,6-dinitroaniline, 3,5-dinitroaniline, and N,N-dimethyl-toludine), diphenyl(p-tolyl)amine, methyldiphenylamine, triphenylamine, phenylenediamine, naphthylamine, diamino-naphthalene, pyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole, 2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazole derivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g., thiazole and isothiazole), imidazole derivatives (e.g., imidazole, 4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazole derivatives, furazan derivatives, pyrroline derivatives (e.g., pyrroline and 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine, N-methylpyrrolidine, pyrrolidinone, and N-methlpyrrolidone), imidazoline derivatives, imidazolidine derivatives, pyridine derivatives (e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine, butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine, trimethylpyridine, triethylpyridine, phenylpyridine, 3-methyl-2-phenylpyridine, 4-tert-butylpyridine, diphenylpyridine, benzylpyridine, methoxypyridine, butoxypyridine, dimethoxypyridine, 1-methyl-2-pyridone, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine, 2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine), pyridazine derivatives, pyrimi-dine derivatives, pyrazine derivatives, pyrazoline derivatives, pyrazolidine derivatives, piperidine derivatives, piperazine derivatives, morpholine derivatives, indole derivatives, isoindole derivatives, 1H-indazole derivatives, indoline derivatives, quinoline derivatives (e.g., quinoline and 3-quinolinecarbonitrile), isoquinoline derivatives, cinnoline derivatives, quinazoline derivatives, quinoxaline derivatives, phthalazine derivatives, purine derivatives, pteridine derivatives, carbazole derivatives, phenanthridine derivatives, acridine derivatives, phenazine derivatives, 1,10-phenanthroline derivatives, adenine derivatives, adenosine derivatives, guanine derivatives, guanosine derivatives, uracil derivatives, and uridine derivatives.
Examples of suitable carboxyl group-bearing nitrogenous compounds include aminobenzoic acid, indolecarboxylic acid, and amino acid derivatives (e.g. nicotinic acid, alanine, alginine, aspartic acid, glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine, methionine, phenylalanine, threonine, lysine, 3-aminopyrazine-2-carboxylic acid, and methoxyalanine). Examples of suitable sulfonyl group-bearing nitrogenous compounds include 3-pyridinesulfonic acid and pyridinium p-toluenesulfonate. Examples of suitable hydroxyl group-bearing nitrogenous compounds, hydroxyphenyl group-bearing nitrogenous compounds, and alcoholic nitrogenous compounds include 2-hydroxypyridine, aminocresol, 2,4-quinolinediol, 3-indolemethanol hydrate, monoethanolamine, diethanolamine, triethanolamine, N-ethyldiethanolamine, N,N-diethylethanolamine, trilsopropanolamine, 2,2xe2x80x2-iminodiethanol, 2-aminoethanol, 3-amino-1-propanol, 4-amino-1-butanol, 4-(2-hydroxyethyl)morpholine, 2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl)piperazine, 1-[2-(2-hydroxyethoxy)ethyl]piperazine, piperidine ethanol, 1-(2-hydroxyethyl)pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone, 3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol, 8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidine ethanol, 1-aziridine ethanol, N-(2-hydroxyethyl)phthalimide, and N-(2-hydroxyethyl)isonicotinamide. Examples of suitable amide derivatives include formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, and benzamide. Suitable -imide derivatives include phthalimide, succinimide, and maleimide.
In addition, basic compounds of the following general formulas (15) and (16) may also be included. 
In the formulas, R41, R42 R43 R47 and R48 are independently straight, branched or cyclic alkylenes of 1 to 20 carbon atoms; R44, R45, R46, R49 and R50 are hydrogen, alkyls of 1 to 20 carbon atoms, or amino; R44 and R45, R45 and R46, R44 and R46, R44 with R45 and R46, and R49 and R50 may bond together to form rings; and S, T and U are each integers from 0 to 20, with the proviso that hydrogen is excluded from R44, R45, R46, R49 and R50 when S, T and U are equal to 0.
The alkylene groups represented by R41, R42, R43, R47 and R48 preferably have 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms, and most preferably 1 to 8 carbon atoms. Examples include methylene, ethylene, n-propylene, isopropylene, n-butylene, isobutylene, n-pentylene, isopentylene, hexylene, nonylene, decylene, cyclopentylene, and cyclohexylene.
The alkyl groups represented by R44, R45, R46, R49 and R50 preferably have 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms, and may be straight, branched or cyclic. Examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, hexyl, nonyl, decyl, dodecyl, tridecyl, cyclopentyl, and cyclohexyl.
Where R44 and R45, R45 and R46, R44 and R46, R44 with R45 and R46, and R49 and R50 form rings, the rings preferably have 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms, and may have branching alkyl groups of 1 to 6 carbon atoms, and especially 1 to 4 carbon atoms.
S, T, and U are each integers from 0 to 20, preferably from 1 to 10, and more preferably from 1 to 8.
Illustrative examples of the compounds of formulas (15) and (16) include tris{2-(methoxymethoxy)ethyl}amine, tris{2-(methoxyethoxy)ethyl}amine, tris[2-{(2-methoxy-ethoxy)methoxy}ethyl]amine, tris{2-(2-methoxyethoxy)-ethyl}amine, tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine, tris(2-(1-ethoxypropoxy)-ethyllamine, tris[2-{(2-hydroxyethoxy)ethoxy}ethyl]amine, 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, 4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane, 1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane, 1-aza-12-crown-4, 1-aza-15-crown-5, and 1-aza-18-crown-6. Especially preferred basic compounds are tertiary amines, aniline derivatives, pyrrolidine derivatives, pyridine derivatives, quinoline derivatives, amino acid derivatives, hydroxyl group-bearing nitrogenous compounds, hydroxyphenyl group-bearing nitrogenous compounds, alcoholic nitrogenous compounds, amide derivatives, imide derivatives, tris{2-(methoxymethoxy)ethyl}amine, tris{2-2-methoxyethoxy)-ethyl ethyl}amine, tris[2-{(2-methoxyethoxy)methyl}ethyl]amine, and 1-aza-15-crown-5.
The above-described basic compound may be used singly or in combinations of two or more thereof, and is preferably formulated in an amount of 0.01 to 2 parts, and especially 0.01 to 1 part by weight, per 100 parts by weight of all the base resins. At less than 0.01 part, the desired effects of the basic compound would not be apparent, while the use of more than 2 parts would result in too low a sensitivity.
Exemplary, non-limiting aromatic compounds bearing a xe2x95x90Cxe2x80x94COOH group (preferably xe2x80x94R57xe2x80x94COOH wherein R57 is a straight or branched alkylene group having 1 to 10 carbon atoms) which may be formulated as component (G) include one or more compounds selected from Groups I and II below. Including component (G) improves the PED stability of the resist and ameliorates edge roughness on nitride film substrates.
Group I:
Compounds in which some or all of the hydrogen atoms on the phenolic hydroxyl groups of the compounds of general formulas (17) to (26) below have been replaced with xe2x80x94R57xe2x80x94COOH (wherein R57 is a straight or branched alkylene of 1 to 10 carbon atoms), and in which the molar ratio C/(C+D) of phenolic hydroxyl groups (C) to xe2x95x90Cxe2x80x94COOH groups (D) in the molecule is from 0.1 to 1.0. 
In these formulas, R1 is hydrogen or methyl; R51 and R52 are each hydrogen or a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms; R53 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or a (R57)hxe2x80x94COORxe2x80x2 group (Rxe2x80x2 being hydrogen or xe2x80x94R57xe2x80x94COOH); R54 is xe2x80x94(CH2)ixe2x80x94 (where i is 2 to 10), an arylene of 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R55 is an alkylene of 1 to 10 carbon atoms, an arylene of 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R56 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or a hydroxyl-substituted phenyl or naphthyl; R57 is a straight or branched alkylene of 1 to 10 carbon atoms; R58 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or a xe2x80x94R57xe2x80x94COOH group; the letter j is an integer from 0 to 5; u and h are each 0 or 1; s1, t1, s2, t2, s3, t3, s4, and t4 are each numbers which satisfy s1+t1=8, s2+t2=5, s3+t3=4, and s4+t4=6, and are such that each phenyl skeleton has at least one hydroxyl group; xcex2 is a number such that the weight average molecular weight of the compound of formula (21) is from 1,000 to 5,000; and 7 is a number such that the weight average molecular weight of the compound of formula (22) is from 1,000 to 10,000.
Group II:
Compounds of general formulas (27) and (28) below. 
In these formulas, R51, R52, and R57 are as defined above; and s5 and t5 are numbers which satisfy s5xe2x89xa70, t5 xe2x89xa70, and s5+t5=5.
Illustrative, non-limiting examples of compounds suitable as above component (G) include compounds of the general formulas III-1 to III-14 and IV-1 to IV-6 below. 
In the above formulas, Rxe2x80x3 is hydrogen or a CH2COOH group such that the CH2COOH group accounts for 10 to 100 mol % of Rxe2x80x3 in each compound, xcex1 and xcex2 are as defined above. 
The aromatic compound bearing a xe2x95x90Cxe2x80x94COOH group within the molecule may be used singly or as combinations of two or more thereof.
The aromatic compound bearing a xe2x95x90Cxe2x80x94COOH group within the molecule is added in an amount ranging from 0.1 to 5 parts, and preferably 1 to 3 parts by weight, per 100 parts by weight of the base resin. At less than 0.1 part, sufficient improvement would not be achieved with regard to either footing on nitride film substrates or PED improvement. On the other hand, at more than 5 parts, the resolution of the resist material would be unacceptably low.
The resist composition of the invention may further include an UV absorber of component (H) which is typically a compound having a molar absorbance of not more than 10,000 at a wavelength of 248 nm. The inclusion of the UV absorber allows the resist composition to be designed and controlled to have a suitable transmittance for substrates of differing reflectances.
Illustrative examples of the UV absorber include fused polycyclic hydrocarbon derivatives such as pentalene, indene, naphthalene, azulene, heptalene, biphenylene, indacene, fluorene, phenalene, phenanthrene, anthracene, fluoranthene, acephenanthrylene, aceanthrylene, triphenylene, pyrene, chrysene, pleiadene, picene, perylene, pentaphene, pentacene, benzophenanthrene, anthraquinone, anthrone, benzanthrone, 2,7-dimethoxynaphthalene, 2-ethyl-9,10-dimethoxyanthracene, 9,10-dimethylanthracene, 9-ethoxyanthracene, 1,2-naphthoquinone, 9-fluorene, and the compounds of general formulas (29) and (30) below; fused heterocyclic derivatives such as thioxanthene-9-one, thianthrene, and dibenzothiophene; benzophenone derivatives such as 2,3,4-trihydroxybenzophenone, 2,3,4,4xe2x80x2-tetrahydroxybenzophenone, 2,4-dihydroxybenzophenone, 3,5-dihydroxybenzophenone, 4,4xe2x80x2-dihydroxybenzophenone, and 4,4xe2x80x2-bis(dimethylamino)-benzophenone; and squaric acid derivatives such as squaric acid and dimethyl squarate. 
In the formulas, R61 to R63 are independently hydrogen, straight or branched alkyl, straight or branched alkoxy, straight or branched alkoxyalkyl, straight or branched alkenyl, or aryl. R64 is a substituted or unsubstituted divalent aliphatic hydrocarbon group which may contain an oxygen atom, a substituted or unsubstituted divalent alicyclic hydrocarbon group which may contain an oxygen atom, a substituted or unsubstituted divalent aromatic hydrocarbon group which may contain an oxygen atom, or an oxygen atom. Also, R65 is an acid labile group; the letter J is 0 or 1; E, F, and G are each 0 or integers from 1 to 9; H is a positive integer from 1 to 10; and E+F+G+H xe2x89xa610.
More particularly, in above formulas (29) and (30), R61 to R63 are independently hydrogen, straight or branched alkyl, straight or branched alkoxy, straight or branched alkoxyalkyl, straight or branched alkenyl, or aryl. Preferable examples of the straight or branched alkyl groups include those having 1 to 10 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, hexyl, cyclohexyl, and adamantyl; of these, the use of methyl, ethyl, isopropyl, or tert-butyl is especially preferred. Preferable examples of straight or branched alkoxy groups include those having 1 to 8 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, hexyloxy, and cyclohexyloxy; of these, the use of methoxy, ethoxy, isopropoxy, and tert-butoxy is especially preferred. Preferable examples of the straight or branched alkoxyalkyl groups include those having 2 to 10 carbon atoms, such as methoxymethyl, 1-ethoxyethyl, 1-ethoxypropyl, 1-propoxyethyl, and tert-butoxyethyl; of these, the use of methoxymethyl, 1-ethoxyethyl, 1-ethoxypropyl, and 1-propoxyethyl is especially preferred. Preferable examples of the straight or branched alkenyl groups include those having 2 to 4 carbon atoms, such as vinyl, propenyl, allyl, and butenyl. Preferable examples of the aryl groups include those having 6 to 14 carbon atoms, such as phenyl, xylyl, toluyl, and cumenyl.
R64 is a substituted or unsubstituted divalent aliphatic hydrocarbon group which may contain an oxygen atom, a substituted or unsubstituted divalent alicyclic hydrocarbon group which may contain an oxygen atom, a substituted or unsubstituted divalent aromatic hydrocarbon group which may contain an oxygen atom, or an oxygen atom; and J in the formula is 0 or 1. When J is 0, the xe2x80x94R64xe2x80x94linkage is a single bond.
Preferable examples of substituted or unsubstituted divalent aliphatic hydrocarbon groups which may contain an oxygen atom include those having 1 to 10 carbon atoms, such as methylene, ethylene, n-propylene, isopropylene, n-butylene, sec-butylene, xe2x80x94CH2Oxe2x80x94, xe2x80x94CH2CH2Oxe2x80x94, and xe2x80x94CH2OCH2xe2x80x94. Of these, methylene, ethylene, xe2x80x94CH2Oxe2x80x94, and xe2x80x94CH2CH2Oxe2x80x94 are preferable.
Preferable examples of substituted or unsubstituted divalent alicyclic hydrocarbon groups which may contain an oxygen atom include those having 5 to 10 carbon atoms, such as 1,4-cyclohexylene, 2-oxacyclohexan-1,4-ylene, and 2-thiacyclohexan-1,4-ylene.
Preferable examples of substituted or unsubstituted divalent aromatic hydrocarbon groups which may contain an oxygen atom include those having 6 to 14 carbon atoms, such as o-phenylene, p-phenylene, 1,2-xylen-3,6-ylene, toluen-2,5-ylene, and 1-cumen-2,5-ylene; and allylalkylene groups having 6 to 14 carbon atoms, such as xe2x80x94CH2Ph- , xe2x80x94CH2PhCH2xe2x80x94, xe2x80x94CH2Ph-, and xe2x80x94OCH2PhCH2Oxe2x80x94 (wherein Ph stands for phenylene).
R65 is an acid labile group, the term xe2x80x9cacid labile groupxe2x80x9d referring here to a moiety in which a carboxyl group has been substituted with one or more functional groups cleavable in the presence of an acid. This may be any moiety which cleaves in the presence of an acid to liberate an alkali-soluble functional group, although moieties having general formula (31a), (31b), or (31c) below are preferred. 
In the formulas, R66 to R69 are independently hydrogen or a straight or branched alkyl, straight or branched alkoxy, straight or branched alkoxyalkyl, straight or branched alkenyl, or aryl, any of which groups may have a carbonyl on the chain thereof, provided that R66 to R69 are not all hydrogen. R66 and R67 may bond together to form a ring. R69 is a straight or branched alkyl, straight or branched alkoxyalkyl, straight or branched alkenyl, or aryl, any of which may have a carbonyl on the chain thereof. R69 may bond with R66 to form a ring.
These straight or branched alkyl, straight or branched alkoxy, straight or branched alkoxyalkyl, straight or branched alkenyl, and aryl groups are exemplified by the same groups mentioned above for R61 to R63.
Examples of rings formed by the combination of R66 and R67 in formula (31a) include those having 4 to 10 carbon atoms, such as cyclohexylidene, cyclopentylidene, 3-oxocyclohexylidene, 3-oxo-4-oxacyclohexylidene, and 4-methylcyclohexylidene.
Examples of rings formed by the combination of R66 and R67 in formula (31b) include those having 3 to 9 carbon atoms, such as 1-silachlorohexylidene, 1-silacyclopentylidene 3-oxo-1-silacyclopentylidene, and 4-methyl-1-silacyclopentylidene.
Examples of rings formed by the combination of R69 and R66 in formula (31c) include those having 4 to 10 carbon atoms, such as 2-oxacyclohexylidene, 2-oxacyclopentylidene, and 2-oxa-4-methylcyclohexylidene.
Exemplary groups represented by the formula (31a) include tertiary alkyl groups having 4 to 10 carbon atoms, such as tert-amyl, 1,1-dimethylethyl, 1,1-dimethylbutyl, 1-ethyl-1-methylpropyl, and 1,1-diethylpropyl; and 3-oxoalkyl groups, such as 1,1-dimethyl-3-oxobutyl, 3-oxocyclohexyl, and 1-methyl-3-oxo-4-oxacyclohexyl.
Exemplary groups represented by the formula (31b) include trialkylsilyl groups having 3 to 10 carbon atoms, such as trimethylsilyl, ethyldimethylsilyl, dimethylpropylsily, diethylmethylsilyl, triethylsilyl, and tert-butyldimethylsilyl.
Exemplary groups represented by the formula (31c) include groups having 2 to 8 carbon atoms, such as 1-methoxymethyl, 1-methoxyethyl, 1-ethoxyethyl, 1-ethoxypropyl, 1-ethoxyisobutyl, 1-n-propoxyethyl, 1-tert-butoxyethyl, 1-n-butoxyethyl, 1-isobutoxyethyl, 1-tert-pentoxyethyl, 1-cyclohexyloxyethyl, 1-(2xe2x80x2-n-butoxyethoxy)-ethyl, 1-(2xe2x80x2-ethylhexyloxy)ethyl, 1-{4xe2x80x2-(acetoxymethyl)-cyclohexylmethyloxy}ethyl, 1-{4xe2x80x2-(tert-butoxycarbonyloxy-methyl)cyclohexylmethyloxy}ethyl, 2-methoxy-2-methylethyl, 1-ethoxypropyl, dimethoxymethyl, diethoxymethyl, tetrahydrofuranyl, and tetrahydropyranyl.
In above formulas (29) and (30), E, F and G are each 0 or positive integers from 1 to 9, and H is a positive integer from 1 to 10, so as to satisfy E+F+G+H xe2x89xa610.
Preferable examples of compounds represented by formulas (29) and (30) include the compounds shown in formulas (32a) to (32j) below. 
In these formulas, R70 is an acid labile group.
Further examples of the UV absorber include diarylsulfoxide derivatives such as bis(4-hydroxyphenyl) sulfoxide, bis(4-tert-butoxyphenyl)sulfoxide, bis(4-tert-butoxycarbonyloxyphenyl)sulfoxide, and bis[4-(1-ethoxyethoxy)phenyl]sulfoxide; diarylsulfone derivatives such as bis(4-hydroxyphenyl)sulfone, bis(4-tert-butoxyphenyl)sulfone, bis(4-tert-butoxycarbonyloxyphenyl)-sulfone, bis[4-(1-ethoxyethoxy)phenyl]sulfone, and bis[4-(1-ethoxypropoxy)phenyl]sulfone; diazo compounds such as benzoquinonediazide, naphthoquinonediazide, anthraquinonediazide, diazofluorene, diazotetralone, and diazophenanthrone; and quinonediazide group-containing compounds such as the complete or partial ester compounds of naphthoquinone-1,2-diazide-5-sulfonate chloride with 2,3,4-trihydroxybenzophenone, and the complete or partial ester compounds of 2-diazide-4-sulfonate chloride with 2,4,4xe2x80x2-trihydroxybenzophenone.
Preferable examples of the UV absorber include tert-butyl 9-anthracenecarboxylate, tert-amyl 9-anthracene-carboxylate, tert-methoxymethyl 9-anthracenecarboxylate, tert-ethoxyethyl 9-anthracenecarboxylate, tert-tetrahydro-pyranyl 9-anthracenecarboxylate, tert-tetrahydrofuranyl 9-anthracenecarboxylate, and partial ester compounds of naphthoquinone-1,2-diazide-5-sulfonate chloride with 2,3,4-trihydroxybenzophenone.
The UV absorber used as component (H) is included in an amount of preferably 0 to 10 parts, more preferably 0.5 to 10 parts, and even more preferably 1 to 5 parts by weight, per 100 parts by weight of the base resin.
The resist composition of the invention may additionally include, as component (I), an acetylene alcohol derivative for the purpose of enhancing the shelf stability.
Examples of compounds preferred for use as the acetylene alcohol derivative include those having general formulas (33) and (34) below. 
In the formulas, R71, R72, R73, R74, and R75 are each hydrogen or a straight, branched, or cyclic alkyl of 1 to 8 carbon atoms; and X and Y are each 0 or a positive integer, satisfying 0xe2x89xa6Xxe2x89xa630, 0xe2x89xa6Yxe2x89xa630, and 0xe2x89xa6X+Yxe2x89xa640.
Preferable examples of the acetylene alcohol derivative include Surfynol 61, Surfynol 82, Surfynol 104, Surfynol 104E, Surfynol 104H, Surfynol 104A, Surfynol TG, Surfynol PC, Surfynol 440, Surfynol 465, and Surfynol 485 from Air Products and Chemicals Inc., and Olfin E1004 from Nisshin Chemical Industry K.K.
The acetylene alcohol derivative is added in an amount of preferably 0.01 to 2% by weight, and more preferably 0.02 to 1% by weight, per 100% by weight of the resist composition. Less than 0.01% by weight would be ineffective for improving coating characteristics and shelf stability, whereas more than 2% by weight would result in a resist having a low resolution.
The resist composition of the invention may include, as an optional ingredient, a surfactant which is commonly used for improving the coating characteristics. Optional ingredients may be added in conventional amounts so long as this does not compromise the objects of the invention.
A nonionic surfactant is preferred, examples of which include perfluoroalkyl polyoxyethylene ethanols, fluorinated alkyl esters, perfluoroalkylamine oxides, and fluorinated organosiloxane compounds. Illustrative examples include Florade FC-430 and FC-431 from Sumitomo 3M Ltd., Surflon S-141, S-145, S-381 and S-383 from Asahi Glass Co., Ltd., Unidyne DS-401, DS-403, and DS-451 from Daikin Industries Ltd., Megafac F-8151, F-171, F-172, F-173 and F-177 from Dainippon Ink and Chemicals, Inc., and X-70-092 and X-70-093 from Shin-Etsu Chemical Co., Ltd. Preferred surfactants include Florade FC-430 from Sumitomo 3M Ltd. and X-70-093 from Shin-Etsu Chemical Co., Ltd.
Pattern formation using the chemical amplification positive resist composition of the invention may be carried out by a known lithographic technique. For example, the resist composition may be applied onto a substrate such as a silicon wafer by spin coating or the like to form a resist film having a thickness of 0.5 to 2.0 xcexcm, which is then pre-baked on a hot plate at 60 to 150xc2x0 C. for 1 to 10 minutes, and preferably at 80 to 120xc2x0 C. for 1 to 5 minutes. A patterning mask having the desired pattern may then be placed over the resist film, and the film exposed through the mask to an electron beam or to high-energy radiation such as deep-UV rays having a wavelength below 300 nm, an excimer laser, or x-rays in a dose of about 1 to 200 mJ/cm2, and preferably about 10 to 100 mJ/cm2, then post-exposure baked (PEB) on a hot plate at 60 to 150xc2x0 C. for 1 to 5 minutes, and preferably at 80 to 120xc2x0 C. for 1 to 3 minutes. Finally, development may be carried out using as the developer an aqueous alkali solution, such as 0.1 to 5%, and preferably 2 to 3%, tetramethylammonium hydroxide (TMAH), this being done by a conventional method such as dipping, puddling, or spraying for a period of 0.1 to 3 minutes, and preferably 0.5 to 2 minutes. These steps result in the formation of the desired pattern on the substrate. Of the various types of high-energy radiation that may be used, the resist composition of the invention is best suited to fine pattern formation with, in particular, deep-UV rays having a wavelength of 193 to 254 nm, an excimer laser, x-rays, or an electron beam. The desired pattern may not be obtainable outside the upper and lower limits of the above range.
The chemical amplification type positive working resist composition comprising the polymer of the invention is sensitive to high-energy radiation, has excellent sensitivity, resolution, and plasma etching resistance, and provides a resist pattern of outstanding thermal stability and reproducibility. Moreover, the resulting pattern is less prone to overhang formation and has an excellent dimensional controllability. The additional formulation of an acetylene alcohol derivative improves shelf stability. Because these features of the inventive resist composition enable its use particularly as a resist having a low absorption at the exposure wavelength of a KrF excimer laser, a finely defined pattern having sidewalls perpendicular to the substrate can easily be formed, making the resist ideal as a micropatterning material in VLSI fabrication.